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 $68.60   12.233%   $76.9918   $76.99   $77.00   $77.00  
  Purchase #2 $55.94   7.590%   $60.1858   $60.19   $60.20   $60.20  
  Purchase #3 $116.94   9.335%   $127.8563   $127.86   $127.85   $127.90  
  Purchase #4 $214.63   3.575%   $222.303   $222.30   $222.30   $222.30  
  Purchase #5 $37.46   11.218%   $41.6623   $41.66   $41.65   $41.70  
  Purchase #6 $214.66   3.244%   $221.6236   $221.62   $221.60   $221.60  
  Purchase #7 $176.44   7.361%   $189.4277   $189.43   $189.45   $189.40  
  7 purchase totals = $884.67       $940.0505   $940.05   $940.05   $940.10