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 $241.67   10.153%   $266.2068   $266.21   $266.20   $266.20  
  Purchase #2 $222.95   11.507%   $248.6049   $248.60   $248.60   $248.60  
  Purchase #3 $94.96   3.103%   $97.9066   $97.91   $97.90   $97.90  
  Purchase #4 $19.99   11.450%   $22.2789   $22.28   $22.30   $22.30  
  Purchase #5 $225.80   10.185%   $248.7977   $248.80   $248.80   $248.80  
  Purchase #6 $213.89   11.486%   $238.4574   $238.46   $238.45   $238.50  
  Purchase #7 $56.35   13.602%   $64.0147   $64.01   $64.00   $64.00  
  7 purchase totals = $1,075.61       $1,186.2670   $1,186.27   $1,186.25   $1,186.30