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 $248.30   7.663%   $267.3272   $267.33   $267.35   $267.30  
  Purchase #2 $138.77   11.264%   $154.4011   $154.40   $154.40   $154.40  
  Purchase #3 $102.77   3.328%   $106.1902   $106.19   $106.20   $106.20  
  Purchase #4 $64.67   4.632%   $67.6655   $67.67   $67.65   $67.70  
  Purchase #5 $19.94   7.471%   $21.4297   $21.43   $21.45   $21.40  
  Purchase #6 $94.28   3.694%   $97.7627   $97.76   $97.75   $97.80  
  Purchase #7 $28.45   10.869%   $31.5422   $31.54   $31.55   $31.50  
  7 purchase totals = $697.18       $746.3186   $746.32   $746.35   $746.30