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 $119.89   11.552%   $133.7397   $133.74   $133.75   $133.70  
  Purchase #2 $46.89   5.475%   $49.4572   $49.46   $49.45   $49.50  
  Purchase #3 $115.55   4.416%   $120.6527   $120.65   $120.65   $120.70  
  Purchase #4 $64.62   10.545%   $71.4342   $71.43   $71.45   $71.40  
  Purchase #5 $142.32   6.296%   $151.2805   $151.28   $151.30   $151.30  
  Purchase #6 $135.43   13.764%   $154.0706   $154.07   $154.05   $154.10  
  Purchase #7 $241.58   12.320%   $271.3427   $271.34   $271.35   $271.30  
  7 purchase totals = $866.28       $951.9776   $951.97   $952.00   $952.00