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 $8.42   3.321%   $8.6996   $8.70   $8.70   $8.70  
  Purchase #2 $113.82   3.234%   $117.5009   $117.50   $117.50   $117.50  
  Purchase #3 $66.84   9.518%   $73.2018   $73.20   $73.20   $73.20  
  Purchase #4 $130.46   3.857%   $135.4918   $135.49   $135.50   $135.50  
  Purchase #5 $160.44   9.219%   $175.231   $175.23   $175.25   $175.20  
  Purchase #6 $48.93   5.615%   $51.6774   $51.68   $51.70   $51.70  
  Purchase #7 $18.37   8.346%   $19.9032   $19.90   $19.90   $19.90  
  7 purchase totals = $547.28       $581.7057   $581.70   $581.75   $581.70