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 $59.94   10.692%   $66.3488   $66.35   $66.35   $66.30  
  Purchase #2 $26.68   5.807%   $28.2293   $28.23   $28.25   $28.20  
  Purchase #3 $33.57   7.581%   $36.1149   $36.11   $36.10   $36.10  
  Purchase #4 $213.36   13.383%   $241.914   $241.91   $241.90   $241.90  
  Purchase #5 $50.36   6.113%   $53.4385   $53.44   $53.45   $53.40  
  Purchase #6 $33.61   6.829%   $35.9052   $35.91   $35.90   $35.90  
  Purchase #7 $191.30   11.494%   $213.288   $213.29   $213.30   $213.30  
  7 purchase totals = $608.82       $675.2387   $675.24   $675.25   $675.10