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 $248.49   7.565%   $267.2883   $267.29   $267.30   $267.30  
  Purchase #2 $92.40   6.389%   $98.3034   $98.30   $98.30   $98.30  
  Purchase #3 $74.78   3.542%   $77.4287   $77.43   $77.45   $77.40  
  Purchase #4 $180.29   3.853%   $187.2366   $187.24   $187.25   $187.20  
  Purchase #5 $214.40   12.594%   $241.4015   $241.40   $241.40   $241.40  
  Purchase #6 $9.81   6.190%   $10.4172   $10.42   $10.40   $10.40  
  Purchase #7 $190.32   10.290%   $209.9039   $209.90   $209.90   $209.90  
  7 purchase totals = $1,010.49       $1,091.9796   $1,091.98   $1,092.00   $1,091.90