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 $231.72   7.874%   $249.9656   $249.97   $249.95   $250.00  
  Purchase #2 $46.50   13.412%   $52.7366   $52.74   $52.75   $52.70  
  Purchase #3 $212.38   11.239%   $236.2494   $236.25   $236.25   $236.20  
  Purchase #4 $84.54   11.237%   $94.0398   $94.04   $94.05   $94.00  
  Purchase #5 $232.99   8.802%   $253.4978   $253.50   $253.50   $253.50  
  Purchase #6 $205.55   5.151%   $216.1379   $216.14   $216.15   $216.10  
  Purchase #7 $59.69   10.399%   $65.8972   $65.90   $65.90   $65.90  
  7 purchase totals = $1,073.37       $1,168.5243   $1,168.54   $1,168.55   $1,168.40