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 $86.68   8.804%   $94.3113   $94.31   $94.30   $94.30  
  Purchase #2 $164.99   11.493%   $183.9523   $183.95   $183.95   $184.00  
  Purchase #3 $74.80   10.335%   $82.5306   $82.53   $82.55   $82.50  
  Purchase #4 $78.80   12.122%   $88.3521   $88.35   $88.35   $88.40  
  Purchase #5 $34.84   4.167%   $36.2918   $36.29   $36.30   $36.30  
  Purchase #6 $147.33   4.785%   $154.3797   $154.38   $154.40   $154.40  
  Purchase #7 $153.82   8.508%   $166.907   $166.91   $166.90   $166.90  
  7 purchase totals = $741.26       $806.7248   $806.72   $806.75   $806.80