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 $206.76   12.256%   $232.1005   $232.10   $232.10   $232.10  
  Purchase #2 $33.42   5.192%   $35.1552   $35.16   $35.15   $35.20  
  Purchase #3 $137.42   11.358%   $153.0282   $153.03   $153.05   $153.00  
  Purchase #4 $45.44   12.535%   $51.1359   $51.14   $51.15   $51.10  
  Purchase #5 $210.49   9.657%   $230.817   $230.82   $230.80   $230.80  
  Purchase #6 $31.85   5.580%   $33.6272   $33.63   $33.65   $33.60  
  Purchase #7 $26.46   4.319%   $27.6028   $27.60   $27.60   $27.60  
  7 purchase totals = $691.84       $763.4668   $763.48   $763.50   $763.40