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 $65.89   11.420%   $73.4146   $73.41   $73.40   $73.40  
  Purchase #2 $246.71   9.108%   $269.1803   $269.18   $269.20   $269.20  
  Purchase #3 $54.27   9.136%   $59.2281   $59.23   $59.25   $59.20  
  Purchase #4 $104.99   11.313%   $116.8675   $116.87   $116.85   $116.90  
  Purchase #5 $50.52   13.174%   $57.1755   $57.18   $57.20   $57.20  
  Purchase #6 $95.48   6.498%   $101.6843   $101.68   $101.70   $101.70  
  Purchase #7 $247.66   13.648%   $281.4606   $281.46   $281.45   $281.50  
  7 purchase totals = $865.52       $959.0109   $959.01   $959.05   $959.10