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 $246.55   8.609%   $267.7755   $267.78   $267.80   $267.80  
  Purchase #2 $135.25   3.395%   $139.8417   $139.84   $139.85   $139.80  
  Purchase #3 $191.55   4.134%   $199.4687   $199.47   $199.45   $199.50  
  Purchase #4 $198.44   10.245%   $218.7702   $218.77   $218.75   $218.80  
  Purchase #5 $164.93   6.209%   $175.1705   $175.17   $175.15   $175.20  
  Purchase #6 $54.70   4.578%   $57.2042   $57.20   $57.20   $57.20  
  Purchase #7 $192.49   8.654%   $209.1481   $209.15   $209.15   $209.10  
  7 purchase totals = $1,183.91       $1,267.3789   $1,267.38   $1,267.35   $1,267.40