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 $222.96   11.696%   $249.0374   $249.04   $249.05   $249.00  
  Purchase #2 $147.40   9.189%   $160.9446   $160.94   $160.95   $160.90  
  Purchase #3 $95.34   10.184%   $105.0494   $105.05   $105.05   $105.00  
  Purchase #4 $59.88   4.324%   $62.4692   $62.47   $62.45   $62.50  
  Purchase #5 $194.94   4.229%   $203.184   $203.18   $203.20   $203.20  
  Purchase #6 $66.36   12.533%   $74.6769   $74.68   $74.70   $74.70  
  Purchase #7 $143.72   9.334%   $157.1348   $157.13   $157.15   $157.10  
  7 purchase totals = $930.60       $1,012.4963   $1,012.49   $1,012.55   $1,012.40