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 $7.36   3.388%   $7.6094   $7.61   $7.60   $7.60  
  Purchase #2 $211.69   13.727%   $240.7487   $240.75   $240.75   $240.70  
  Purchase #3 $19.49   3.158%   $20.1055   $20.11   $20.10   $20.10  
  Purchase #4 $88.50   9.304%   $96.734   $96.73   $96.75   $96.70  
  Purchase #5 $174.89   4.666%   $183.0504   $183.05   $183.05   $183.10  
  Purchase #6 $154.51   9.520%   $169.2194   $169.22   $169.20   $169.20  
  Purchase #7 $46.77   5.106%   $49.1581   $49.16   $49.15   $49.20  
  7 purchase totals = $703.21       $766.6255   $766.63   $766.60   $766.60