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 $9.85   10.765%   $10.9104   $10.91   $10.90   $10.90  
  Purchase #2 $109.30   6.191%   $116.0668   $116.07   $116.05   $116.10  
  Purchase #3 $194.66   12.462%   $218.9185   $218.92   $218.90   $218.90  
  Purchase #4 $92.44   4.871%   $96.9428   $96.94   $96.95   $96.90  
  Purchase #5 $85.32   12.792%   $96.2341   $96.23   $96.25   $96.20  
  Purchase #6 $108.45   7.368%   $116.4406   $116.44   $116.45   $116.40  
  Purchase #7 $182.36   8.643%   $198.1214   $198.12   $198.10   $198.10  
  7 purchase totals = $782.38       $853.6346   $853.63   $853.60   $853.50