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 $84.31   10.208%   $92.9164   $92.92   $92.90   $92.90  
  Purchase #2 $112.69   6.153%   $119.6238   $119.62   $119.60   $119.60  
  Purchase #3 $18.68   13.121%   $21.131   $21.13   $21.15   $21.10  
  Purchase #4 $213.44   6.328%   $226.9465   $226.95   $226.95   $226.90  
  Purchase #5 $187.73   10.105%   $206.7001   $206.70   $206.70   $206.70  
  Purchase #6 $58.99   6.790%   $62.9954   $63.00   $63.00   $63.00  
  Purchase #7 $166.49   9.835%   $182.8643   $182.86   $182.85   $182.90  
  7 purchase totals = $842.33       $913.1775   $913.18   $913.15   $913.10