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 $192.71   8.198%   $208.5084   $208.51   $208.50   $208.50  
  Purchase #2 $183.35   11.596%   $204.6113   $204.61   $204.60   $204.60  
  Purchase #3 $117.78   11.498%   $131.3223   $131.32   $131.30   $131.30  
  Purchase #4 $240.75   9.637%   $263.9511   $263.95   $263.95   $264.00  
  Purchase #5 $250.26   7.222%   $268.3338   $268.33   $268.35   $268.30  
  Purchase #6 $193.56   12.272%   $217.3137   $217.31   $217.30   $217.30  
  Purchase #7 $161.92   11.292%   $180.204   $180.20   $180.20   $180.20  
  7 purchase totals = $1,340.33       $1,474.2446   $1,474.23   $1,474.20   $1,474.20