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 $54.85   12.839%   $61.8922   $61.89   $61.90   $61.90  
  Purchase #2 $224.62   7.480%   $241.4216   $241.42   $241.40   $241.40  
  Purchase #3 $12.44   6.543%   $13.2539   $13.25   $13.25   $13.30  
  Purchase #4 $39.75   4.170%   $41.4076   $41.41   $41.40   $41.40  
  Purchase #5 $143.98   6.677%   $153.5935   $153.59   $153.60   $153.60  
  Purchase #6 $5.97   5.689%   $6.3096   $6.31   $6.30   $6.30  
  Purchase #7 $234.94   8.583%   $255.1049   $255.10   $255.10   $255.10  
  7 purchase totals = $716.55       $772.9833   $772.97   $772.95   $773.00