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 $104.99   10.554%   $116.0706   $116.07   $116.05   $116.10  
  Purchase #2 $245.94   7.199%   $263.6452   $263.65   $263.65   $263.60  
  Purchase #3 $19.73   4.237%   $20.566   $20.57   $20.55   $20.60  
  Purchase #4 $13.67   12.397%   $15.3647   $15.36   $15.35   $15.40  
  Purchase #5 $85.83   4.713%   $89.8752   $89.88   $89.90   $89.90  
  Purchase #6 $186.64   11.519%   $208.1391   $208.14   $208.15   $208.10  
  Purchase #7 $220.44   13.481%   $250.1575   $250.16   $250.15   $250.20  
  7 purchase totals = $877.24       $963.8183   $963.83   $963.80   $963.90