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 $60.67   10.206%   $66.862   $66.86   $66.85   $66.90  
  Purchase #2 $154.95   6.196%   $164.5507   $164.55   $164.55   $164.60  
  Purchase #3 $51.53   12.870%   $58.1619   $58.16   $58.15   $58.20  
  Purchase #4 $146.54   11.227%   $162.992   $162.99   $163.00   $163.00  
  Purchase #5 $159.94   3.328%   $165.2628   $165.26   $165.25   $165.30  
  Purchase #6 $98.79   8.223%   $106.9135   $106.91   $106.90   $106.90  
  Purchase #7 $220.55   5.528%   $232.742   $232.74   $232.75   $232.70  
  7 purchase totals = $892.97       $957.4849   $957.47   $957.45   $957.60