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 $95.49   9.152%   $104.2292   $104.23   $104.25   $104.20  
  Purchase #2 $180.57   11.613%   $201.5396   $201.54   $201.55   $201.50  
  Purchase #3 $86.45   13.674%   $98.2712   $98.27   $98.25   $98.30  
  Purchase #4 $70.85   5.653%   $74.8552   $74.86   $74.85   $74.90  
  Purchase #5 $103.95   8.814%   $113.1122   $113.11   $113.10   $113.10  
  Purchase #6 $93.59   11.762%   $104.5981   $104.60   $104.60   $104.60  
  Purchase #7 $13.54   11.773%   $15.1341   $15.13   $15.15   $15.10  
  7 purchase totals = $644.44       $711.7396   $711.74   $711.75   $711.70