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 $47.62   6.240%   $50.5915   $50.59   $50.60   $50.60  
  Purchase #2 $214.71   12.357%   $241.2417   $241.24   $241.25   $241.20  
  Purchase #3 $67.25   10.460%   $74.2844   $74.28   $74.30   $74.30  
  Purchase #4 $202.92   6.212%   $215.5254   $215.53   $215.55   $215.50  
  Purchase #5 $35.92   4.830%   $37.6549   $37.65   $37.65   $37.70  
  Purchase #6 $246.59   5.398%   $259.9009   $259.90   $259.90   $259.90  
  Purchase #7 $242.40   6.763%   $258.7935   $258.79   $258.80   $258.80  
  7 purchase totals = $1,057.41       $1,137.9923   $1,137.98   $1,138.05   $1,138.00