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 $58.45   7.478%   $62.8209   $62.82   $62.80   $62.80  
  Purchase #2 $176.87   10.633%   $195.6766   $195.68   $195.70   $195.70  
  Purchase #3 $109.26   10.654%   $120.9006   $120.90   $120.90   $120.90  
  Purchase #4 $205.45   10.855%   $227.7516   $227.75   $227.75   $227.80  
  Purchase #5 $81.46   5.639%   $86.0535   $86.05   $86.05   $86.10  
  Purchase #6 $81.53   9.748%   $89.4775   $89.48   $89.50   $89.50  
  Purchase #7 $16.89   4.772%   $17.696   $17.70   $17.70   $17.70  
  7 purchase totals = $729.91       $800.3767   $800.38   $800.40   $800.50