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 $241.87   7.578%   $260.1989   $260.20   $260.20   $260.20  
  Purchase #2 $36.42   12.652%   $41.0279   $41.03   $41.05   $41.00  
  Purchase #3 $10.76   10.845%   $11.9269   $11.93   $11.95   $11.90  
  Purchase #4 $206.91   4.181%   $215.5609   $215.56   $215.55   $215.60  
  Purchase #5 $102.82   12.554%   $115.728   $115.73   $115.75   $115.70  
  Purchase #6 $114.64   9.608%   $125.6546   $125.65   $125.65   $125.70  
  Purchase #7 $213.77   13.306%   $242.2142   $242.21   $242.20   $242.20  
  7 purchase totals = $927.19       $1,012.3114   $1,012.31   $1,012.35   $1,012.30