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 $181.26   12.471%   $203.8649   $203.86   $203.85   $203.90  
  Purchase #2 $213.25   9.342%   $233.1718   $233.17   $233.15   $233.20  
  Purchase #3 $133.41   11.872%   $149.2484   $149.25   $149.25   $149.20  
  Purchase #4 $240.37   5.450%   $253.4702   $253.47   $253.45   $253.50  
  Purchase #5 $22.31   6.833%   $23.8344   $23.83   $23.85   $23.80  
  Purchase #6 $50.73   11.133%   $56.3778   $56.38   $56.40   $56.40  
  Purchase #7 $43.71   11.180%   $48.5968   $48.60   $48.60   $48.60  
  7 purchase totals = $885.04       $968.5643   $968.56   $968.55   $968.60