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 $94.43   4.688%   $98.8569   $98.86   $98.85   $98.90  
  Purchase #2 $111.99   10.821%   $124.1084   $124.11   $124.10   $124.10  
  Purchase #3 $160.70   7.270%   $172.3829   $172.38   $172.40   $172.40  
  Purchase #4 $169.70   8.853%   $184.7235   $184.72   $184.70   $184.70  
  Purchase #5 $214.66   8.825%   $233.6037   $233.60   $233.60   $233.60  
  Purchase #6 $61.98   3.501%   $64.1499   $64.15   $64.15   $64.10  
  Purchase #7 $171.29   3.510%   $177.3023   $177.30   $177.30   $177.30  
  7 purchase totals = $984.75       $1,055.1276   $1,055.12   $1,055.10   $1,055.10