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 $247.83   6.128%   $263.017   $263.02   $263.00   $263.00  
  Purchase #2 $13.41   13.389%   $15.2055   $15.21   $15.20   $15.20  
  Purchase #3 $186.99   4.633%   $195.6532   $195.65   $195.65   $195.70  
  Purchase #4 $102.89   8.129%   $111.2539   $111.25   $111.25   $111.30  
  Purchase #5 $194.44   12.375%   $218.502   $218.50   $218.50   $218.50  
  Purchase #6 $231.62   12.572%   $260.7393   $260.74   $260.75   $260.70  
  Purchase #7 $53.47   10.418%   $59.0405   $59.04   $59.05   $59.00  
  7 purchase totals = $1,030.65       $1,123.4114   $1,123.41   $1,123.40   $1,123.40