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 $244.78   9.718%   $268.5677   $268.57   $268.55   $268.60  
  Purchase #2 $52.36   7.440%   $56.2556   $56.26   $56.25   $56.30  
  Purchase #3 $189.36   4.361%   $197.618   $197.62   $197.60   $197.60  
  Purchase #4 $37.30   11.738%   $41.6783   $41.68   $41.70   $41.70  
  Purchase #5 $196.91   12.318%   $221.1654   $221.17   $221.15   $221.20  
  Purchase #6 $203.30   5.703%   $214.8942   $214.89   $214.90   $214.90  
  Purchase #7 $20.89   5.565%   $22.0525   $22.05   $22.05   $22.10  
  7 purchase totals = $944.90       $1,022.2317   $1,022.24   $1,022.20   $1,022.40