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 $100.55   10.760%   $111.3692   $111.37   $111.35   $111.40  
  Purchase #2 $91.44   13.130%   $103.4461   $103.45   $103.45   $103.40  
  Purchase #3 $118.74   5.639%   $125.4357   $125.44   $125.45   $125.40  
  Purchase #4 $244.66   4.214%   $254.97   $254.97   $254.95   $255.00  
  Purchase #5 $223.32   4.618%   $233.6329   $233.63   $233.65   $233.60  
  Purchase #6 $182.59   6.261%   $194.022   $194.02   $194.00   $194.00  
  Purchase #7 $155.93   9.271%   $170.3863   $170.39   $170.40   $170.40  
  7 purchase totals = $1,117.23       $1,193.2622   $1,193.27   $1,193.25   $1,193.20