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 $87.36   10.471%   $96.5075   $96.51   $96.50   $96.50  
  Purchase #2 $100.66   13.525%   $114.2743   $114.27   $114.25   $114.30  
  Purchase #3 $34.73   7.341%   $37.2795   $37.28   $37.30   $37.30  
  Purchase #4 $48.46   10.382%   $53.4911   $53.49   $53.50   $53.50  
  Purchase #5 $70.72   4.677%   $74.0276   $74.03   $74.05   $74.00  
  Purchase #6 $96.48   10.454%   $106.566   $106.57   $106.55   $106.60  
  Purchase #7 $221.41   5.770%   $234.1854   $234.19   $234.20   $234.20  
  7 purchase totals = $659.82       $716.3314   $716.34   $716.35   $716.40