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 $68.84   12.644%   $77.5441   $77.54   $77.55   $77.50  
  Purchase #2 $214.89   7.814%   $231.6815   $231.68   $231.70   $231.70  
  Purchase #3 $42.46   11.391%   $47.2966   $47.30   $47.30   $47.30  
  Purchase #4 $210.81   5.871%   $223.1867   $223.19   $223.20   $223.20  
  Purchase #5 $210.27   12.411%   $236.3666   $236.37   $236.35   $236.40  
  Purchase #6 $71.43   3.527%   $73.9493   $73.95   $73.95   $73.90  
  Purchase #7 $139.70   7.824%   $150.6301   $150.63   $150.65   $150.60  
  7 purchase totals = $958.40       $1,040.6549   $1,040.66   $1,040.70   $1,040.60