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 $204.79   10.437%   $226.1639   $226.16   $226.15   $226.20  
  Purchase #2 $33.38   11.841%   $37.3325   $37.33   $37.35   $37.30  
  Purchase #3 $82.77   6.454%   $88.112   $88.11   $88.10   $88.10  
  Purchase #4 $139.31   4.850%   $146.0665   $146.07   $146.05   $146.10  
  Purchase #5 $229.53   13.865%   $261.3543   $261.35   $261.35   $261.40  
  Purchase #6 $92.62   5.705%   $97.904   $97.90   $97.90   $97.90  
  Purchase #7 $105.98   10.403%   $117.0051   $117.01   $117.00   $117.00  
  7 purchase totals = $888.38       $973.9383   $973.93   $973.90   $974.00