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 $66.53   13.464%   $75.4876   $75.49   $75.50   $75.50  
  Purchase #2 $46.51   8.590%   $50.5052   $50.51   $50.50   $50.50  
  Purchase #3 $230.79   6.857%   $246.6153   $246.62   $246.60   $246.60  
  Purchase #4 $32.49   6.342%   $34.5505   $34.55   $34.55   $34.60  
  Purchase #5 $190.47   3.255%   $196.6698   $196.67   $196.65   $196.70  
  Purchase #6 $124.45   12.726%   $140.2875   $140.29   $140.30   $140.30  
  Purchase #7 $187.67   12.768%   $211.6317   $211.63   $211.65   $211.60  
  7 purchase totals = $878.91       $955.7476   $955.76   $955.75   $955.80