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 $144.73   7.114%   $155.0261   $155.03   $155.05   $155.00  
  Purchase #2 $8.42   8.504%   $9.136   $9.14   $9.15   $9.10  
  Purchase #3 $44.73   13.188%   $50.629   $50.63   $50.65   $50.60  
  Purchase #4 $236.41   8.371%   $256.1999   $256.20   $256.20   $256.20  
  Purchase #5 $224.34   10.605%   $248.1313   $248.13   $248.15   $248.10  
  Purchase #6 $8.33   9.375%   $9.1109   $9.11   $9.10   $9.10  
  Purchase #7 $48.71   3.790%   $50.5561   $50.56   $50.55   $50.60  
  7 purchase totals = $715.67       $778.7893   $778.80   $778.85   $778.70