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 $146.99   8.773%   $159.8854   $159.89   $159.90   $159.90  
  Purchase #2 $32.92   4.192%   $34.3   $34.30   $34.30   $34.30  
  Purchase #3 $144.37   8.192%   $156.1968   $156.20   $156.20   $156.20  
  Purchase #4 $216.56   10.589%   $239.4915   $239.49   $239.50   $239.50  
  Purchase #5 $73.33   5.822%   $77.5993   $77.60   $77.60   $77.60  
  Purchase #6 $163.51   13.155%   $185.0197   $185.02   $185.00   $185.00  
  Purchase #7 $90.55   10.702%   $100.2407   $100.24   $100.25   $100.20  
  7 purchase totals = $868.23       $952.7334   $952.74   $952.75   $952.70