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 $223.61   11.814%   $250.0273   $250.03   $250.05   $250.00  
  Purchase #2 $207.34   10.268%   $228.6297   $228.63   $228.65   $228.60  
  Purchase #3 $207.90   4.237%   $216.7087   $216.71   $216.70   $216.70  
  Purchase #4 $105.88   8.685%   $115.0757   $115.08   $115.10   $115.10  
  Purchase #5 $113.64   7.499%   $122.1619   $122.16   $122.15   $122.20  
  Purchase #6 $216.71   4.112%   $225.6211   $225.62   $225.60   $225.60  
  Purchase #7 $132.79   12.350%   $149.1896   $149.19   $149.20   $149.20  
  7 purchase totals = $1,207.87       $1,307.4140   $1,307.42   $1,307.45   $1,307.40