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 $67.43   11.351%   $75.084   $75.08   $75.10   $75.10  
  Purchase #2 $66.92   4.495%   $69.9281   $69.93   $69.95   $69.90  
  Purchase #3 $145.32   7.177%   $155.7496   $155.75   $155.75   $155.70  
  Purchase #4 $49.88   8.424%   $54.0819   $54.08   $54.10   $54.10  
  Purchase #5 $73.47   6.428%   $78.1927   $78.19   $78.20   $78.20  
  Purchase #6 $54.97   13.251%   $62.2541   $62.25   $62.25   $62.30  
  Purchase #7 $250.48   5.454%   $264.1412   $264.14   $264.15   $264.10  
  7 purchase totals = $708.47       $759.4316   $759.42   $759.50   $759.40