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 $94.67   10.361%   $104.4788   $104.48   $104.50   $104.50  
  Purchase #2 $184.99   12.715%   $208.5115   $208.51   $208.50   $208.50  
  Purchase #3 $110.91   5.142%   $116.613   $116.61   $116.60   $116.60  
  Purchase #4 $238.97   11.468%   $266.3751   $266.38   $266.40   $266.40  
  Purchase #5 $76.46   8.670%   $83.0891   $83.09   $83.10   $83.10  
  Purchase #6 $109.37   5.848%   $115.766   $115.77   $115.75   $115.80  
  Purchase #7 $162.26   8.456%   $175.9807   $175.98   $176.00   $176.00  
  7 purchase totals = $977.63       $1,070.8142   $1,070.82   $1,070.85   $1,070.90