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 $57.29   8.874%   $62.3739   $62.37   $62.35   $62.40  
  Purchase #2 $212.33   13.728%   $241.4787   $241.48   $241.50   $241.50  
  Purchase #3 $27.67   9.364%   $30.261   $30.26   $30.25   $30.30  
  Purchase #4 $161.36   4.768%   $169.0536   $169.05   $169.05   $169.10  
  Purchase #5 $199.98   7.267%   $214.5125   $214.51   $214.50   $214.50  
  Purchase #6 $22.39   4.860%   $23.4782   $23.48   $23.50   $23.50  
  Purchase #7 $6.49   12.787%   $7.3199   $7.32   $7.30   $7.30  
  7 purchase totals = $687.51       $748.4778   $748.47   $748.45   $748.60