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 $63.50   4.168%   $66.1467   $66.15   $66.15   $66.10  
  Purchase #2 $142.70   7.748%   $153.7564   $153.76   $153.75   $153.80  
  Purchase #3 $157.58   10.171%   $173.6075   $173.61   $173.60   $173.60  
  Purchase #4 $44.82   5.581%   $47.3214   $47.32   $47.30   $47.30  
  Purchase #5 $43.36   10.777%   $48.0329   $48.03   $48.05   $48.00  
  Purchase #6 $68.76   9.162%   $75.0598   $75.06   $75.05   $75.10  
  Purchase #7 $186.61   7.178%   $200.0049   $200.00   $200.00   $200.00  
  7 purchase totals = $707.33       $763.9296   $763.93   $763.90   $763.90