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 $167.97   5.537%   $177.2705   $177.27   $177.25   $177.30  
  Purchase #2 $187.67   3.505%   $194.2478   $194.25   $194.25   $194.20  
  Purchase #3 $126.32   5.319%   $133.039   $133.04   $133.05   $133.00  
  Purchase #4 $247.59   6.506%   $263.6982   $263.70   $263.70   $263.70  
  Purchase #5 $117.59   9.520%   $128.7846   $128.78   $128.80   $128.80  
  Purchase #6 $189.94   10.247%   $209.4032   $209.40   $209.40   $209.40  
  Purchase #7 $109.36   8.507%   $118.6633   $118.66   $118.65   $118.70  
  7 purchase totals = $1,146.44       $1,225.1066   $1,225.10   $1,225.10   $1,225.10