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 $14.71   8.757%   $15.9982   $16.00   $16.00   $16.00  
  Purchase #2 $140.93   4.219%   $146.8758   $146.88   $146.90   $146.90  
  Purchase #3 $205.70   7.285%   $220.6852   $220.69   $220.70   $220.70  
  Purchase #4 $44.66   7.158%   $47.8568   $47.86   $47.85   $47.90  
  Purchase #5 $184.92   12.141%   $207.3711   $207.37   $207.35   $207.40  
  Purchase #6 $241.31   11.179%   $268.286   $268.29   $268.30   $268.30  
  Purchase #7 $111.71   3.653%   $115.7908   $115.79   $115.80   $115.80  
  7 purchase totals = $943.94       $1,022.8639   $1,022.88   $1,022.90   $1,023.00