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 $62.77   5.602%   $66.2864   $66.29   $66.30   $66.30  
  Purchase #2 $79.55   9.869%   $87.4008   $87.40   $87.40   $87.40  
  Purchase #3 $214.30   4.224%   $223.352   $223.35   $223.35   $223.40  
  Purchase #4 $233.34   5.456%   $246.071   $246.07   $246.05   $246.10  
  Purchase #5 $21.25   7.686%   $22.8833   $22.88   $22.90   $22.90  
  Purchase #6 $96.51   5.224%   $101.5517   $101.55   $101.55   $101.60  
  Purchase #7 $196.83   8.762%   $214.0762   $214.08   $214.10   $214.10  
  7 purchase totals = $904.55       $961.6214   $961.62   $961.65   $961.80