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 $46.27   5.521%   $48.8246   $48.82   $48.80   $48.80  
  Purchase #2 $16.76   9.202%   $18.3023   $18.30   $18.30   $18.30  
  Purchase #3 $56.79   6.475%   $60.4672   $60.47   $60.45   $60.50  
  Purchase #4 $27.44   8.827%   $29.8621   $29.86   $29.85   $29.90  
  Purchase #5 $33.41   8.734%   $36.328   $36.33   $36.35   $36.30  
  Purchase #6 $86.50   10.303%   $95.4121   $95.41   $95.40   $95.40  
  Purchase #7 $11.89   5.423%   $12.5348   $12.53   $12.55   $12.50  
  7 purchase totals = $279.06       $301.7311   $301.72   $301.70   $301.70