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 $67.49   6.559%   $71.9167   $71.92   $71.90   $71.90  
  Purchase #2 $14.96   3.230%   $15.4432   $15.44   $15.45   $15.40  
  Purchase #3 $185.44   3.548%   $192.0194   $192.02   $192.00   $192.00  
  Purchase #4 $246.43   4.709%   $258.0344   $258.03   $258.05   $258.00  
  Purchase #5 $183.73   11.325%   $204.5374   $204.54   $204.55   $204.50  
  Purchase #6 $118.65   4.748%   $124.2835   $124.28   $124.30   $124.30  
  Purchase #7 $139.77   6.439%   $148.7698   $148.77   $148.75   $148.80  
  7 purchase totals = $956.47       $1,015.0044   $1,015.00   $1,015.00   $1,014.90