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 $119.51   5.247%   $125.7807   $125.78   $125.80   $125.80  
  Purchase #2 $233.60   3.155%   $240.9701   $240.97   $240.95   $241.00  
  Purchase #3 $194.44   8.120%   $210.2285   $210.23   $210.25   $210.20  
  Purchase #4 $56.25   9.631%   $61.6674   $61.67   $61.65   $61.70  
  Purchase #5 $242.77   9.394%   $265.5758   $265.58   $265.60   $265.60  
  Purchase #6 $190.83   13.465%   $216.5253   $216.53   $216.55   $216.50  
  Purchase #7 $241.64   13.693%   $274.7278   $274.73   $274.75   $274.70  
  7 purchase totals = $1,279.04       $1,395.4756   $1,395.49   $1,395.55   $1,395.50