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 $15.35   8.725%   $16.6893   $16.69   $16.70   $16.70  
  Purchase #2 $245.61   10.702%   $271.8952   $271.90   $271.90   $271.90  
  Purchase #3 $5.45   3.631%   $5.6479   $5.65   $5.65   $5.60  
  Purchase #4 $218.71   3.175%   $225.654   $225.65   $225.65   $225.70  
  Purchase #5 $101.68   10.233%   $112.0849   $112.08   $112.10   $112.10  
  Purchase #6 $213.63   9.374%   $233.6557   $233.66   $233.65   $233.70  
  Purchase #7 $84.51   5.314%   $89.0009   $89.00   $89.00   $89.00  
  7 purchase totals = $884.94       $954.6279   $954.63   $954.65   $954.70