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 $232.64   3.587%   $240.9848   $240.98   $241.00   $241.00  
  Purchase #2 $227.99   12.352%   $256.1513   $256.15   $256.15   $256.20  
  Purchase #3 $156.46   5.370%   $164.8619   $164.86   $164.85   $164.90  
  Purchase #4 $125.71   6.304%   $133.6348   $133.63   $133.65   $133.60  
  Purchase #5 $218.82   8.278%   $236.9339   $236.93   $236.95   $236.90  
  Purchase #6 $110.32   8.237%   $119.4071   $119.41   $119.40   $119.40  
  Purchase #7 $155.90   7.266%   $167.2277   $167.23   $167.25   $167.20  
  7 purchase totals = $1,227.84       $1,319.2015   $1,319.19   $1,319.25   $1,319.20