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 $75.26   10.160%   $82.9064   $82.91   $82.90   $82.90  
  Purchase #2 $96.32   6.267%   $102.3564   $102.36   $102.35   $102.40  
  Purchase #3 $117.78   12.873%   $132.9418   $132.94   $132.95   $132.90  
  Purchase #4 $230.87   13.314%   $261.608   $261.61   $261.60   $261.60  
  Purchase #5 $66.55   3.638%   $68.9711   $68.97   $68.95   $69.00  
  Purchase #6 $212.27   11.361%   $236.386   $236.39   $236.40   $236.40  
  Purchase #7 $87.92   10.662%   $97.294   $97.29   $97.30   $97.30  
  7 purchase totals = $886.97       $982.4637   $982.47   $982.45   $982.50