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 $244.51   4.279%   $254.9726   $254.97   $254.95   $255.00  
  Purchase #2 $224.77   7.318%   $241.2187   $241.22   $241.20   $241.20  
  Purchase #3 $55.80   9.413%   $61.0525   $61.05   $61.05   $61.10  
  Purchase #4 $245.87   5.712%   $259.9141   $259.91   $259.90   $259.90  
  Purchase #5 $156.87   10.749%   $173.732   $173.73   $173.75   $173.70  
  Purchase #6 $78.49   10.469%   $86.7071   $86.71   $86.70   $86.70  
  Purchase #7 $121.65   12.625%   $137.0083   $137.01   $137.00   $137.00  
  7 purchase totals = $1,127.96       $1,214.6053   $1,214.60   $1,214.55   $1,214.60