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 $65.36   12.544%   $73.5588   $73.56   $73.55   $73.60  
  Purchase #2 $160.34   8.489%   $173.9513   $173.95   $173.95   $174.00  
  Purchase #3 $206.80   6.107%   $219.4293   $219.43   $219.45   $219.40  
  Purchase #4 $210.85   5.215%   $221.8458   $221.85   $221.85   $221.80  
  Purchase #5 $56.66   6.789%   $60.5066   $60.51   $60.50   $60.50  
  Purchase #6 $126.78   8.159%   $137.124   $137.12   $137.10   $137.10  
  Purchase #7 $197.95   9.536%   $216.8265   $216.83   $216.85   $216.80  
  7 purchase totals = $1,024.74       $1,103.2423   $1,103.25   $1,103.25   $1,103.20