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 $208.64   7.369%   $224.0147   $224.01   $224.00   $224.00  
  Purchase #2 $57.49   10.588%   $63.577   $63.58   $63.60   $63.60  
  Purchase #3 $47.62   10.408%   $52.5763   $52.58   $52.60   $52.60  
  Purchase #4 $92.89   12.851%   $104.8273   $104.83   $104.85   $104.80  
  Purchase #5 $124.50   10.692%   $137.8115   $137.81   $137.80   $137.80  
  Purchase #6 $122.42   7.795%   $131.9626   $131.96   $131.95   $132.00  
  Purchase #7 $29.87   11.302%   $33.2459   $33.25   $33.25   $33.20  
  7 purchase totals = $683.43       $748.0153   $748.02   $748.05   $748.00