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 $59.92   5.764%   $63.3738   $63.37   $63.35   $63.40  
  Purchase #2 $178.64   10.732%   $197.8116   $197.81   $197.80   $197.80  
  Purchase #3 $17.63   7.842%   $19.0125   $19.01   $19.00   $19.00  
  Purchase #4 $54.68   5.308%   $57.5824   $57.58   $57.60   $57.60  
  Purchase #5 $239.90   11.742%   $268.0691   $268.07   $268.05   $268.10  
  Purchase #6 $232.84   12.183%   $261.2069   $261.21   $261.20   $261.20  
  Purchase #7 $99.44   7.222%   $106.6216   $106.62   $106.60   $106.60  
  7 purchase totals = $883.05       $973.6779   $973.67   $973.60   $973.70