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 $243.78   11.849%   $272.6655   $272.67   $272.65   $272.70  
  Purchase #2 $229.65   13.522%   $260.7033   $260.70   $260.70   $260.70  
  Purchase #3 $213.27   8.646%   $231.7093   $231.71   $231.70   $231.70  
  Purchase #4 $59.89   11.709%   $66.9025   $66.90   $66.90   $66.90  
  Purchase #5 $153.44   9.790%   $168.4618   $168.46   $168.45   $168.50  
  Purchase #6 $160.82   5.855%   $170.236   $170.24   $170.25   $170.20  
  Purchase #7 $21.82   13.344%   $24.7317   $24.73   $24.75   $24.70  
  7 purchase totals = $1,082.67       $1,195.4101   $1,195.41   $1,195.40   $1,195.40