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 $152.94   6.497%   $162.8765   $162.88   $162.90   $162.90  
  Purchase #2 $13.64   5.185%   $14.3472   $14.35   $14.35   $14.30  
  Purchase #3 $161.69   5.115%   $169.9604   $169.96   $169.95   $170.00  
  Purchase #4 $35.80   6.458%   $38.112   $38.11   $38.10   $38.10  
  Purchase #5 $188.76   10.569%   $208.71   $208.71   $208.70   $208.70  
  Purchase #6 $34.29   13.584%   $38.948   $38.95   $38.95   $38.90  
  Purchase #7 $241.54   11.822%   $270.0949   $270.09   $270.10   $270.10  
  7 purchase totals = $828.66       $903.0490   $903.05   $903.05   $903.00