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 $61.88   7.355%   $66.4313   $66.43   $66.45   $66.40  
  Purchase #2 $248.93   11.279%   $277.0068   $277.01   $277.00   $277.00  
  Purchase #3 $175.28   5.863%   $185.5567   $185.56   $185.55   $185.60  
  Purchase #4 $38.98   10.776%   $43.1805   $43.18   $43.20   $43.20  
  Purchase #5 $14.30   5.493%   $15.0855   $15.09   $15.10   $15.10  
  Purchase #6 $163.94   9.146%   $178.934   $178.93   $178.95   $178.90  
  Purchase #7 $44.85   8.130%   $48.4963   $48.50   $48.50   $48.50  
  7 purchase totals = $748.16       $814.6911   $814.70   $814.75   $814.70