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 $83.46   10.836%   $92.5037   $92.50   $92.50   $92.50  
  Purchase #2 $102.88   3.288%   $106.2627   $106.26   $106.25   $106.30  
  Purchase #3 $12.87   11.585%   $14.361   $14.36   $14.35   $14.40  
  Purchase #4 $20.93   9.367%   $22.8905   $22.89   $22.90   $22.90  
  Purchase #5 $119.36   3.352%   $123.3609   $123.36   $123.35   $123.40  
  Purchase #6 $35.73   3.389%   $36.9409   $36.94   $36.95   $36.90  
  Purchase #7 $213.59   10.613%   $236.2583   $236.26   $236.25   $236.30  
  7 purchase totals = $588.82       $632.5780   $632.57   $632.55   $632.70