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 $44.86   8.429%   $48.6412   $48.64   $48.65   $48.60  
  Purchase #2 $71.98   5.812%   $76.1635   $76.16   $76.15   $76.20  
  Purchase #3 $120.35   9.388%   $131.6485   $131.65   $131.65   $131.60  
  Purchase #4 $191.55   3.422%   $198.1048   $198.10   $198.10   $198.10  
  Purchase #5 $46.69   10.655%   $51.6648   $51.66   $51.65   $51.70  
  Purchase #6 $172.26   5.731%   $182.1322   $182.13   $182.15   $182.10  
  Purchase #7 $70.44   6.587%   $75.0799   $75.08   $75.10   $75.10  
  7 purchase totals = $718.13       $763.4349   $763.42   $763.45   $763.40