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 $46.41   12.244%   $52.0924   $52.09   $52.10   $52.10  
  Purchase #2 $93.35   8.492%   $101.2773   $101.28   $101.30   $101.30  
  Purchase #3 $172.95   7.865%   $186.5525   $186.55   $186.55   $186.60  
  Purchase #4 $65.68   9.580%   $71.9721   $71.97   $71.95   $72.00  
  Purchase #5 $205.33   11.281%   $228.4933   $228.49   $228.50   $228.50  
  Purchase #6 $26.46   13.262%   $29.9691   $29.97   $29.95   $30.00  
  Purchase #7 $72.94   13.111%   $82.5032   $82.50   $82.50   $82.50  
  7 purchase totals = $683.12       $752.8599   $752.85   $752.85   $753.00