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 $244.98   8.560%   $265.9503   $265.95   $265.95   $266.00  
  Purchase #2 $83.88   4.595%   $87.7343   $87.73   $87.75   $87.70  
  Purchase #3 $238.80   9.389%   $261.2209   $261.22   $261.20   $261.20  
  Purchase #4 $94.25   10.239%   $103.9003   $103.90   $103.90   $103.90  
  Purchase #5 $147.28   5.317%   $155.1109   $155.11   $155.10   $155.10  
  Purchase #6 $86.98   12.791%   $98.1056   $98.11   $98.10   $98.10  
  Purchase #7 $180.77   3.176%   $186.5113   $186.51   $186.50   $186.50  
  7 purchase totals = $1,076.94       $1,158.5336   $1,158.53   $1,158.50   $1,158.50