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 $213.94   10.377%   $236.1406   $236.14   $236.15   $236.10  
  Purchase #2 $132.40   13.209%   $149.8887   $149.89   $149.90   $149.90  
  Purchase #3 $24.78   8.430%   $26.869   $26.87   $26.85   $26.90  
  Purchase #4 $29.44   7.809%   $31.739   $31.74   $31.75   $31.70  
  Purchase #5 $59.72   9.126%   $65.17   $65.17   $65.15   $65.20  
  Purchase #6 $237.64   10.403%   $262.3617   $262.36   $262.35   $262.40  
  Purchase #7 $24.76   6.586%   $26.3907   $26.39   $26.40   $26.40  
  7 purchase totals = $722.68       $798.5597   $798.56   $798.55   $798.60