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 $192.93   7.313%   $207.039   $207.04   $207.05   $207.00  
  Purchase #2 $72.86   4.721%   $76.2997   $76.30   $76.30   $76.30  
  Purchase #3 $131.36   13.780%   $149.4614   $149.46   $149.45   $149.50  
  Purchase #4 $44.77   10.706%   $49.5631   $49.56   $49.55   $49.60  
  Purchase #5 $233.41   3.766%   $242.2002   $242.20   $242.20   $242.20  
  Purchase #6 $151.77   6.822%   $162.1237   $162.12   $162.10   $162.10  
  Purchase #7 $63.90   9.243%   $69.8063   $69.81   $69.80   $69.80  
  7 purchase totals = $891.00       $956.4934   $956.49   $956.45   $956.50