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 $75.26   12.434%   $84.6178   $84.62   $84.60   $84.60  
  Purchase #2 $41.38   6.228%   $43.9571   $43.96   $43.95   $44.00  
  Purchase #3 $214.86   5.102%   $225.8222   $225.82   $225.80   $225.80  
  Purchase #4 $126.64   3.522%   $131.1003   $131.10   $131.10   $131.10  
  Purchase #5 $92.34   3.341%   $95.4251   $95.43   $95.45   $95.40  
  Purchase #6 $66.50   13.687%   $75.6019   $75.60   $75.60   $75.60  
  Purchase #7 $169.65   7.459%   $182.3042   $182.30   $182.30   $182.30  
  7 purchase totals = $786.63       $838.8286   $838.83   $838.80   $838.80