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 $240.31   8.721%   $261.2674   $261.27   $261.25   $261.30  
  Purchase #2 $238.96   12.480%   $268.7822   $268.78   $268.80   $268.80  
  Purchase #3 $60.91   4.678%   $63.7594   $63.76   $63.75   $63.80  
  Purchase #4 $59.65   4.397%   $62.2728   $62.27   $62.25   $62.30  
  Purchase #5 $112.73   11.574%   $125.7774   $125.78   $125.80   $125.80  
  Purchase #6 $145.72   7.774%   $157.0483   $157.05   $157.05   $157.00  
  Purchase #7 $67.97   6.563%   $72.4309   $72.43   $72.45   $72.40  
  7 purchase totals = $926.25       $1,011.3384   $1,011.34   $1,011.35   $1,011.40