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 $185.42   8.806%   $201.7481   $201.75   $201.75   $201.70  
  Purchase #2 $222.27   13.362%   $251.9697   $251.97   $251.95   $252.00  
  Purchase #3 $175.99   13.507%   $199.761   $199.76   $199.75   $199.80  
  Purchase #4 $170.44   11.545%   $190.1173   $190.12   $190.10   $190.10  
  Purchase #5 $37.38   13.498%   $42.4256   $42.43   $42.45   $42.40  
  Purchase #6 $57.67   12.205%   $64.7086   $64.71   $64.70   $64.70  
  Purchase #7 $131.42   10.547%   $145.2809   $145.28   $145.30   $145.30  
  7 purchase totals = $980.59       $1,096.0112   $1,096.02   $1,096.00   $1,096.00