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 $246.79   5.174%   $259.5589   $259.56   $259.55   $259.60  
  Purchase #2 $92.96   9.643%   $101.9241   $101.92   $101.90   $101.90  
  Purchase #3 $55.69   4.559%   $58.2289   $58.23   $58.25   $58.20  
  Purchase #4 $62.91   13.254%   $71.2481   $71.25   $71.25   $71.20  
  Purchase #5 $166.30   13.219%   $188.2832   $188.28   $188.30   $188.30  
  Purchase #6 $180.56   12.226%   $202.6353   $202.64   $202.65   $202.60  
  Purchase #7 $66.95   9.287%   $73.1676   $73.17   $73.15   $73.20  
  7 purchase totals = $872.16       $955.0461   $955.05   $955.05   $955.00