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 $58.44   9.467%   $63.9725   $63.97   $63.95   $64.00  
  Purchase #2 $150.62   8.208%   $162.9829   $162.98   $163.00   $163.00  
  Purchase #3 $84.31   5.318%   $88.7936   $88.79   $88.80   $88.80  
  Purchase #4 $97.53   3.107%   $100.5603   $100.56   $100.55   $100.60  
  Purchase #5 $247.81   11.353%   $275.9439   $275.94   $275.95   $275.90  
  Purchase #6 $86.76   4.464%   $90.633   $90.63   $90.65   $90.60  
  Purchase #7 $178.77   3.727%   $185.4328   $185.43   $185.45   $185.40  
  7 purchase totals = $904.24       $968.3190   $968.30   $968.35   $968.30