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 $48.67   13.106%   $55.0487   $55.05   $55.05   $55.00  
  Purchase #2 $200.54   4.691%   $209.9473   $209.95   $209.95   $209.90  
  Purchase #3 $185.94   5.529%   $196.2206   $196.22   $196.20   $196.20  
  Purchase #4 $131.78   9.441%   $144.2213   $144.22   $144.20   $144.20  
  Purchase #5 $32.38   11.191%   $36.0036   $36.00   $36.00   $36.00  
  Purchase #6 $5.36   7.708%   $5.7731   $5.77   $5.75   $5.80  
  Purchase #7 $78.36   8.244%   $84.82   $84.82   $84.80   $84.80  
  7 purchase totals = $683.03       $732.0346   $732.03   $731.95   $731.90