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 $62.83   5.324%   $66.1751   $66.18   $66.20   $66.20  
  Purchase #2 $225.54   11.558%   $251.6079   $251.61   $251.60   $251.60  
  Purchase #3 $111.92   8.328%   $121.2407   $121.24   $121.25   $121.20  
  Purchase #4 $10.49   4.707%   $10.9838   $10.98   $11.00   $11.00  
  Purchase #5 $245.39   11.606%   $273.87   $273.87   $273.85   $273.90  
  Purchase #6 $238.49   4.597%   $249.4534   $249.45   $249.45   $249.50  
  Purchase #7 $45.29   8.578%   $49.175   $49.18   $49.20   $49.20  
  7 purchase totals = $939.95       $1,022.5059   $1,022.51   $1,022.55   $1,022.60