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 $214.88   8.161%   $232.4164   $232.42   $232.40   $232.40  
  Purchase #2 $162.38   4.862%   $170.2749   $170.27   $170.25   $170.30  
  Purchase #3 $65.55   13.184%   $74.1921   $74.19   $74.20   $74.20  
  Purchase #4 $82.44   10.202%   $90.8505   $90.85   $90.85   $90.90  
  Purchase #5 $58.69   13.641%   $66.6959   $66.70   $66.70   $66.70  
  Purchase #6 $154.74   9.154%   $168.9049   $168.90   $168.90   $168.90  
  Purchase #7 $202.29   11.498%   $225.5493   $225.55   $225.55   $225.50  
  7 purchase totals = $940.97       $1,028.8840   $1,028.88   $1,028.85   $1,028.90