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 $240.81   9.626%   $263.9904   $263.99   $264.00   $264.00  
  Purchase #2 $117.82   10.637%   $130.3525   $130.35   $130.35   $130.40  
  Purchase #3 $204.90   6.680%   $218.5873   $218.59   $218.60   $218.60  
  Purchase #4 $245.33   11.602%   $273.7932   $273.79   $273.80   $273.80  
  Purchase #5 $238.96   3.337%   $246.9341   $246.93   $246.95   $246.90  
  Purchase #6 $6.69   3.454%   $6.9211   $6.92   $6.90   $6.90  
  Purchase #7 $64.90   6.255%   $68.9595   $68.96   $68.95   $69.00  
  7 purchase totals = $1,119.41       $1,209.5381   $1,209.53   $1,209.55   $1,209.60