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 $247.36   6.159%   $262.5949   $262.59   $262.60   $262.60  
  Purchase #2 $46.97   6.835%   $50.1804   $50.18   $50.20   $50.20  
  Purchase #3 $9.99   3.608%   $10.3504   $10.35   $10.35   $10.40  
  Purchase #4 $230.77   5.596%   $243.6839   $243.68   $243.70   $243.70  
  Purchase #5 $13.78   5.324%   $14.5136   $14.51   $14.50   $14.50  
  Purchase #6 $243.57   7.722%   $262.3785   $262.38   $262.40   $262.40  
  Purchase #7 $163.64   7.442%   $175.8181   $175.82   $175.80   $175.80  
  7 purchase totals = $956.08       $1,019.5198   $1,019.51   $1,019.55   $1,019.60