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 $55.77   4.534%   $58.2986   $58.30   $58.30   $58.30  
  Purchase #2 $68.67   11.189%   $76.3535   $76.35   $76.35   $76.40  
  Purchase #3 $194.88   7.188%   $208.888   $208.89   $208.90   $208.90  
  Purchase #4 $191.34   7.642%   $205.9622   $205.96   $205.95   $206.00  
  Purchase #5 $220.27   7.134%   $235.9841   $235.98   $236.00   $236.00  
  Purchase #6 $83.56   4.506%   $87.3252   $87.33   $87.35   $87.30  
  Purchase #7 $65.76   13.495%   $74.6343   $74.63   $74.65   $74.60  
  7 purchase totals = $880.25       $947.4459   $947.44   $947.50   $947.50