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 $86.76   6.728%   $92.5972   $92.60   $92.60   $92.60  
  Purchase #2 $199.59   6.561%   $212.6851   $212.69   $212.70   $212.70  
  Purchase #3 $124.63   7.522%   $134.0047   $134.00   $134.00   $134.00  
  Purchase #4 $221.98   5.633%   $234.4841   $234.48   $234.50   $234.50  
  Purchase #5 $172.96   6.618%   $184.4065   $184.41   $184.40   $184.40  
  Purchase #6 $40.62   10.590%   $44.9217   $44.92   $44.90   $44.90  
  Purchase #7 $87.95   12.614%   $99.044   $99.04   $99.05   $99.00  
  7 purchase totals = $934.49       $1,002.1433   $1,002.14   $1,002.15   $1,002.10