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 $95.43   6.157%   $101.3056   $101.31   $101.30   $101.30  
  Purchase #2 $130.65   6.701%   $139.4049   $139.40   $139.40   $139.40  
  Purchase #3 $51.37   10.181%   $56.6   $56.60   $56.60   $56.60  
  Purchase #4 $218.84   6.431%   $232.9136   $232.91   $232.90   $232.90  
  Purchase #5 $156.32   12.553%   $175.9428   $175.94   $175.95   $175.90  
  Purchase #6 $34.95   4.343%   $36.4679   $36.47   $36.45   $36.50  
  Purchase #7 $75.71   12.692%   $85.3191   $85.32   $85.30   $85.30  
  7 purchase totals = $763.27       $827.9539   $827.95   $827.90   $827.90