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 $224.51   3.733%   $232.891   $232.89   $232.90   $232.90  
  Purchase #2 $55.43   5.232%   $58.3301   $58.33   $58.35   $58.30  
  Purchase #3 $187.48   11.215%   $208.5059   $208.51   $208.50   $208.50  
  Purchase #4 $195.60   8.260%   $211.7566   $211.76   $211.75   $211.80  
  Purchase #5 $189.33   10.366%   $208.9559   $208.96   $208.95   $209.00  
  Purchase #6 $219.48   9.183%   $239.6348   $239.63   $239.65   $239.60  
  Purchase #7 $16.90   3.682%   $17.5223   $17.52   $17.50   $17.50  
  7 purchase totals = $1,088.73       $1,177.5966   $1,177.60   $1,177.60   $1,177.60