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 $236.99   10.213%   $261.1938   $261.19   $261.20   $261.20  
  Purchase #2 $233.83   5.468%   $246.6158   $246.62   $246.60   $246.60  
  Purchase #3 $57.52   10.211%   $63.3934   $63.39   $63.40   $63.40  
  Purchase #4 $72.54   10.466%   $80.132   $80.13   $80.15   $80.10  
  Purchase #5 $61.45   9.104%   $67.0444   $67.04   $67.05   $67.00  
  Purchase #6 $130.98   3.845%   $136.0162   $136.02   $136.00   $136.00  
  Purchase #7 $153.40   8.802%   $166.9023   $166.90   $166.90   $166.90  
  7 purchase totals = $946.71       $1,021.2979   $1,021.29   $1,021.30   $1,021.20