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 $123.49   8.723%   $134.262   $134.26   $134.25   $134.30  
  Purchase #2 $158.43   5.489%   $167.1262   $167.13   $167.15   $167.10  
  Purchase #3 $170.49   3.146%   $175.8536   $175.85   $175.85   $175.90  
  Purchase #4 $32.38   5.443%   $34.1424   $34.14   $34.15   $34.10  
  Purchase #5 $106.55   5.340%   $112.2398   $112.24   $112.25   $112.20  
  Purchase #6 $121.80   12.423%   $136.9312   $136.93   $136.95   $136.90  
  Purchase #7 $37.37   9.518%   $40.9269   $40.93   $40.95   $40.90  
  7 purchase totals = $750.51       $801.4821   $801.48   $801.55   $801.40