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 $44.38   9.795%   $48.727   $48.73   $48.75   $48.70  
  Purchase #2 $186.78   7.595%   $200.9659   $200.97   $200.95   $201.00  
  Purchase #3 $28.27   7.814%   $30.479   $30.48   $30.50   $30.50  
  Purchase #4 $231.92   6.439%   $246.8533   $246.85   $246.85   $246.90  
  Purchase #5 $16.40   12.341%   $18.4239   $18.42   $18.40   $18.40  
  Purchase #6 $208.30   5.576%   $219.9148   $219.91   $219.90   $219.90  
  Purchase #7 $116.51   12.112%   $130.6217   $130.62   $130.60   $130.60  
  7 purchase totals = $832.56       $895.9856   $895.98   $895.95   $896.00