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 $82.61   13.776%   $93.9904   $93.99   $94.00   $94.00  
  Purchase #2 $69.44   3.205%   $71.6656   $71.67   $71.65   $71.70  
  Purchase #3 $116.69   6.617%   $124.4114   $124.41   $124.40   $124.40  
  Purchase #4 $99.65   7.849%   $107.4715   $107.47   $107.45   $107.50  
  Purchase #5 $73.29   5.392%   $77.2418   $77.24   $77.25   $77.20  
  Purchase #6 $47.63   5.637%   $50.3149   $50.31   $50.30   $50.30  
  Purchase #7 $112.28   3.791%   $116.5365   $116.54   $116.55   $116.50  
  7 purchase totals = $601.59       $641.6321   $641.63   $641.60   $641.60