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 $242.53   4.393%   $253.1843   $253.18   $253.20   $253.20  
  Purchase #2 $236.69   10.263%   $260.9815   $260.98   $261.00   $261.00  
  Purchase #3 $129.59   12.322%   $145.5581   $145.56   $145.55   $145.60  
  Purchase #4 $203.86   7.785%   $219.7305   $219.73   $219.75   $219.70  
  Purchase #5 $20.80   13.849%   $23.6806   $23.68   $23.70   $23.70  
  Purchase #6 $42.65   12.539%   $47.9979   $48.00   $48.00   $48.00  
  Purchase #7 $69.86   4.787%   $73.2042   $73.20   $73.20   $73.20  
  7 purchase totals = $945.98       $1,024.3371   $1,024.33   $1,024.40   $1,024.40