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 $226.80   11.464%   $252.8004   $252.80   $252.80   $252.80  
  Purchase #2 $105.65   12.410%   $118.7612   $118.76   $118.75   $118.80  
  Purchase #3 $46.71   12.788%   $52.6833   $52.68   $52.70   $52.70  
  Purchase #4 $111.50   5.590%   $117.7329   $117.73   $117.75   $117.70  
  Purchase #5 $241.51   6.449%   $257.085   $257.09   $257.10   $257.10  
  Purchase #6 $245.66   5.603%   $259.4243   $259.42   $259.40   $259.40  
  Purchase #7 $199.70   6.753%   $213.1857   $213.19   $213.20   $213.20  
  7 purchase totals = $1,177.53       $1,271.6728   $1,271.67   $1,271.70   $1,271.70