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 $175.69   3.748%   $182.2749   $182.27   $182.25   $182.30  
  Purchase #2 $44.62   9.859%   $49.0191   $49.02   $49.00   $49.00  
  Purchase #3 $16.28   11.429%   $18.1406   $18.14   $18.15   $18.10  
  Purchase #4 $148.97   3.216%   $153.7609   $153.76   $153.75   $153.80  
  Purchase #5 $28.49   3.194%   $29.4   $29.40   $29.40   $29.40  
  Purchase #6 $195.95   3.376%   $202.5653   $202.57   $202.55   $202.60  
  Purchase #7 $87.47   4.175%   $91.1219   $91.12   $91.10   $91.10  
  7 purchase totals = $697.47       $726.2827   $726.28   $726.20   $726.30