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 $162.43   3.811%   $168.6202   $168.62   $168.60   $168.60  
  Purchase #2 $19.77   13.198%   $22.3792   $22.38   $22.40   $22.40  
  Purchase #3 $228.25   7.617%   $245.6358   $245.64   $245.65   $245.60  
  Purchase #4 $245.38   7.803%   $264.527   $264.53   $264.55   $264.50  
  Purchase #5 $91.83   3.336%   $94.8934   $94.89   $94.90   $94.90  
  Purchase #6 $74.68   9.699%   $81.9232   $81.92   $81.90   $81.90  
  Purchase #7 $167.63   8.305%   $181.5517   $181.55   $181.55   $181.60  
  7 purchase totals = $989.97       $1,059.5305   $1,059.53   $1,059.55   $1,059.50