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 $205.26   4.711%   $214.9298   $214.93   $214.95   $214.90  
  Purchase #2 $19.99   11.231%   $22.2351   $22.24   $22.25   $22.20  
  Purchase #3 $50.76   9.745%   $55.7066   $55.71   $55.70   $55.70  
  Purchase #4 $86.85   9.211%   $94.8498   $94.85   $94.85   $94.80  
  Purchase #5 $237.72   5.467%   $250.7162   $250.72   $250.70   $250.70  
  Purchase #6 $155.74   12.551%   $175.2869   $175.29   $175.30   $175.30  
  Purchase #7 $226.40   13.827%   $257.7043   $257.70   $257.70   $257.70  
  7 purchase totals = $982.72       $1,071.4287   $1,071.44   $1,071.45   $1,071.30