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 $64.33   13.639%   $73.104   $73.10   $73.10   $73.10  
  Purchase #2 $241.51   7.767%   $260.2681   $260.27   $260.25   $260.30  
  Purchase #3 $211.92   6.630%   $225.9703   $225.97   $225.95   $226.00  
  Purchase #4 $13.86   4.186%   $14.4402   $14.44   $14.45   $14.40  
  Purchase #5 $87.76   8.189%   $94.9467   $94.95   $94.95   $94.90  
  Purchase #6 $40.98   12.275%   $46.0103   $46.01   $46.00   $46.00  
  Purchase #7 $150.75   10.117%   $166.0014   $166.00   $166.00   $166.00  
  7 purchase totals = $811.11       $880.7410   $880.74   $880.70   $880.70