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 $216.88   12.654%   $244.324   $244.32   $244.30   $244.30  
  Purchase #2 $242.46   12.604%   $273.0197   $273.02   $273.00   $273.00  
  Purchase #3 $78.96   7.182%   $84.6309   $84.63   $84.65   $84.60  
  Purchase #4 $72.42   12.798%   $81.6883   $81.69   $81.70   $81.70  
  Purchase #5 $19.44   6.822%   $20.7662   $20.77   $20.75   $20.80  
  Purchase #6 $46.85   6.102%   $49.7088   $49.71   $49.70   $49.70  
  Purchase #7 $83.56   10.348%   $92.2068   $92.21   $92.20   $92.20  
  7 purchase totals = $760.57       $846.3447   $846.35   $846.30   $846.30