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 $198.75   9.679%   $217.987   $217.99   $218.00   $218.00  
  Purchase #2 $13.91   4.431%   $14.5264   $14.53   $14.55   $14.50  
  Purchase #3 $243.32   7.676%   $261.9972   $262.00   $262.00   $262.00  
  Purchase #4 $32.99   10.466%   $36.4427   $36.44   $36.45   $36.40  
  Purchase #5 $166.43   7.404%   $178.7525   $178.75   $178.75   $178.80  
  Purchase #6 $186.85   12.748%   $210.6696   $210.67   $210.65   $210.70  
  Purchase #7 $241.75   8.776%   $262.966   $262.97   $262.95   $263.00  
  7 purchase totals = $1,084.00       $1,183.3414   $1,183.35   $1,183.35   $1,183.40