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 $86.37   11.677%   $96.4554   $96.46   $96.45   $96.50  
  Purchase #2 $175.47   3.537%   $181.6764   $181.68   $181.70   $181.70  
  Purchase #3 $43.33   10.170%   $47.7367   $47.74   $47.75   $47.70  
  Purchase #4 $22.28   4.317%   $23.2418   $23.24   $23.25   $23.20  
  Purchase #5 $83.57   8.702%   $90.8423   $90.84   $90.85   $90.80  
  Purchase #6 $223.98   11.329%   $249.3547   $249.35   $249.35   $249.40  
  Purchase #7 $45.68   12.652%   $51.4594   $51.46   $51.45   $51.50  
  7 purchase totals = $680.68       $740.7667   $740.77   $740.80   $740.80