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 $226.55   4.466%   $236.6677   $236.67   $236.65   $236.70  
  Purchase #2 $24.49   7.451%   $26.3147   $26.31   $26.30   $26.30  
  Purchase #3 $147.66   11.390%   $164.4785   $164.48   $164.50   $164.50  
  Purchase #4 $17.93   10.124%   $19.7452   $19.75   $19.75   $19.70  
  Purchase #5 $242.64   11.399%   $270.2985   $270.30   $270.30   $270.30  
  Purchase #6 $87.98   10.786%   $97.4695   $97.47   $97.45   $97.50  
  Purchase #7 $215.38   6.742%   $229.9009   $229.90   $229.90   $229.90  
  7 purchase totals = $962.63       $1,044.8750   $1,044.88   $1,044.85   $1,044.90