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 $232.96   8.547%   $252.8711   $252.87   $252.85   $252.90  
  Purchase #2 $182.75   6.111%   $193.9179   $193.92   $193.90   $193.90  
  Purchase #3 $35.40   11.348%   $39.4172   $39.42   $39.40   $39.40  
  Purchase #4 $71.44   10.334%   $78.8226   $78.82   $78.80   $78.80  
  Purchase #5 $233.30   13.470%   $264.7255   $264.73   $264.75   $264.70  
  Purchase #6 $239.48   8.235%   $259.2012   $259.20   $259.20   $259.20  
  Purchase #7 $19.56   12.207%   $21.9477   $21.95   $21.95   $21.90  
  7 purchase totals = $1,014.89       $1,110.9032   $1,110.91   $1,110.85   $1,110.80