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 $67.73   11.213%   $75.3246   $75.32   $75.30   $75.30  
  Purchase #2 $176.55   10.652%   $195.3561   $195.36   $195.35   $195.40  
  Purchase #3 $181.68   13.774%   $206.7046   $206.70   $206.70   $206.70  
  Purchase #4 $238.71   4.656%   $249.8243   $249.82   $249.80   $249.80  
  Purchase #5 $17.43   5.734%   $18.4294   $18.43   $18.45   $18.40  
  Purchase #6 $34.48   5.624%   $36.4192   $36.42   $36.40   $36.40  
  Purchase #7 $174.86   3.593%   $181.1427   $181.14   $181.15   $181.10  
  7 purchase totals = $891.44       $963.2009   $963.19   $963.15   $963.10