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 $92.68   6.482%   $98.6875   $98.69   $98.70   $98.70  
  Purchase #2 $97.39   13.519%   $110.5562   $110.56   $110.55   $110.60  
  Purchase #3 $59.71   11.524%   $66.591   $66.59   $66.60   $66.60  
  Purchase #4 $182.75   6.492%   $194.6141   $194.61   $194.60   $194.60  
  Purchase #5 $7.48   7.466%   $8.0385   $8.04   $8.05   $8.00  
  Purchase #6 $200.44   9.771%   $220.025   $220.03   $220.05   $220.00  
  Purchase #7 $242.28   9.657%   $265.677   $265.68   $265.70   $265.70  
  7 purchase totals = $882.73       $964.1893   $964.20   $964.25   $964.20