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 $55.35   13.707%   $62.9368   $62.94   $62.95   $62.90  
  Purchase #2 $52.83   9.682%   $57.945   $57.95   $57.95   $57.90  
  Purchase #3 $242.38   11.845%   $271.0899   $271.09   $271.10   $271.10  
  Purchase #4 $23.27   12.714%   $26.2285   $26.23   $26.25   $26.20  
  Purchase #5 $84.48   11.189%   $93.9325   $93.93   $93.95   $93.90  
  Purchase #6 $236.57   5.390%   $249.3211   $249.32   $249.30   $249.30  
  Purchase #7 $220.30   8.523%   $239.0762   $239.08   $239.10   $239.10  
  7 purchase totals = $915.18       $1,000.5300   $1,000.54   $1,000.60   $1,000.40