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 $109.74   6.163%   $116.5033   $116.50   $116.50   $116.50  
  Purchase #2 $126.41   9.180%   $138.0144   $138.01   $138.00   $138.00  
  Purchase #3 $32.53   9.551%   $35.6369   $35.64   $35.65   $35.60  
  Purchase #4 $111.46   4.461%   $116.4322   $116.43   $116.45   $116.40  
  Purchase #5 $32.73   9.597%   $35.8711   $35.87   $35.85   $35.90  
  Purchase #6 $235.85   11.358%   $262.6378   $262.64   $262.65   $262.60  
  Purchase #7 $132.63   7.757%   $142.9181   $142.92   $142.90   $142.90  
  7 purchase totals = $781.35       $848.0138   $848.01   $848.00   $847.90