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 $230.70   6.414%   $245.4971   $245.50   $245.50   $245.50  
  Purchase #2 $171.42   13.304%   $194.2257   $194.23   $194.25   $194.20  
  Purchase #3 $94.94   3.268%   $98.0426   $98.04   $98.05   $98.00  
  Purchase #4 $58.64   9.642%   $64.2941   $64.29   $64.30   $64.30  
  Purchase #5 $111.94   9.541%   $122.6202   $122.62   $122.60   $122.60  
  Purchase #6 $224.32   5.243%   $236.0811   $236.08   $236.10   $236.10  
  Purchase #7 $77.66   7.457%   $83.4511   $83.45   $83.45   $83.50  
  7 purchase totals = $969.62       $1,044.2119   $1,044.21   $1,044.25   $1,044.20