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 $163.32   10.401%   $180.3069   $180.31   $180.30   $180.30  
  Purchase #2 $236.98   10.453%   $261.7515   $261.75   $261.75   $261.80  
  Purchase #3 $89.90   8.315%   $97.3752   $97.38   $97.40   $97.40  
  Purchase #4 $116.46   8.634%   $126.5152   $126.52   $126.50   $126.50  
  Purchase #5 $14.79   7.201%   $15.855   $15.86   $15.85   $15.90  
  Purchase #6 $69.99   5.228%   $73.6491   $73.65   $73.65   $73.60  
  Purchase #7 $246.59   8.515%   $267.5871   $267.59   $267.60   $267.60  
  7 purchase totals = $938.03       $1,023.0400   $1,023.06   $1,023.05   $1,023.10