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 $242.98   11.823%   $271.7075   $271.71   $271.70   $271.70  
  Purchase #2 $163.75   10.537%   $181.0043   $181.00   $181.00   $181.00  
  Purchase #3 $159.79   4.793%   $167.4487   $167.45   $167.45   $167.40  
  Purchase #4 $110.38   6.414%   $117.4598   $117.46   $117.45   $117.50  
  Purchase #5 $136.91   8.608%   $148.6952   $148.70   $148.70   $148.70  
  Purchase #6 $97.86   3.844%   $101.6217   $101.62   $101.60   $101.60  
  Purchase #7 $24.87   6.647%   $26.5231   $26.52   $26.50   $26.50  
  7 purchase totals = $936.54       $1,014.4603   $1,014.46   $1,014.40   $1,014.40