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 $228.71   11.598%   $255.2358   $255.24   $255.25   $255.20  
  Purchase #2 $171.46   8.786%   $186.5245   $186.52   $186.50   $186.50  
  Purchase #3 $159.49   5.458%   $168.195   $168.20   $168.20   $168.20  
  Purchase #4 $24.91   5.764%   $26.3458   $26.35   $26.35   $26.30  
  Purchase #5 $94.73   3.191%   $97.7528   $97.75   $97.75   $97.80  
  Purchase #6 $156.68   7.865%   $169.0029   $169.00   $169.00   $169.00  
  Purchase #7 $238.86   8.607%   $259.4187   $259.42   $259.40   $259.40  
  7 purchase totals = $1,074.84       $1,162.4755   $1,162.48   $1,162.45   $1,162.40