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 $66.37   6.199%   $70.4843   $70.48   $70.50   $70.50  
  Purchase #2 $163.87   7.751%   $176.5716   $176.57   $176.55   $176.60  
  Purchase #3 $220.46   13.584%   $250.4073   $250.41   $250.40   $250.40  
  Purchase #4 $88.45   6.727%   $94.4   $94.40   $94.40   $94.40  
  Purchase #5 $195.34   13.133%   $220.994   $220.99   $221.00   $221.00  
  Purchase #6 $248.31   11.154%   $276.0065   $276.01   $276.00   $276.00  
  Purchase #7 $104.30   11.577%   $116.3748   $116.37   $116.35   $116.40  
  7 purchase totals = $1,087.10       $1,205.2385   $1,205.23   $1,205.20   $1,205.30