Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $180.25   13.706%   $204.9551   $204.96   $204.95   $205.00  
  Purchase #2 $171.46   10.676%   $189.7651   $189.77   $189.75   $189.80  
  Purchase #3 $109.98   6.866%   $117.5312   $117.53   $117.55   $117.50  
  Purchase #4 $131.73   13.195%   $149.1118   $149.11   $149.10   $149.10  
  Purchase #5 $230.91   5.867%   $244.4575   $244.46   $244.45   $244.50  
  Purchase #6 $167.45   11.544%   $186.7804   $186.78   $186.80   $186.80  
  Purchase #7 $167.28   11.835%   $187.0776   $187.08   $187.10   $187.10  
  7 purchase totals = $1,159.06       $1,279.6787   $1,279.69   $1,279.70   $1,279.80