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 $243.78   12.536%   $274.3403   $274.34   $274.35   $274.30  
  Purchase #2 $216.89   12.614%   $244.2485   $244.25   $244.25   $244.20  
  Purchase #3 $117.79   10.641%   $130.324   $130.32   $130.30   $130.30  
  Purchase #4 $152.70   3.277%   $157.704   $157.70   $157.70   $157.70  
  Purchase #5 $179.65   4.146%   $187.0983   $187.10   $187.10   $187.10  
  Purchase #6 $46.90   7.601%   $50.4649   $50.46   $50.45   $50.50  
  Purchase #7 $167.49   4.105%   $174.3655   $174.37   $174.35   $174.40  
  7 purchase totals = $1,125.20       $1,218.5455   $1,218.54   $1,218.50   $1,218.50