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 $190.90   13.274%   $216.2401   $216.24   $216.25   $216.20  
  Purchase #2 $150.97   10.317%   $166.5456   $166.55   $166.55   $166.50  
  Purchase #3 $66.36   4.784%   $69.5347   $69.53   $69.55   $69.50  
  Purchase #4 $64.72   13.676%   $73.5711   $73.57   $73.55   $73.60  
  Purchase #5 $76.41   12.567%   $86.0124   $86.01   $86.00   $86.00  
  Purchase #6 $190.73   4.289%   $198.9104   $198.91   $198.90   $198.90  
  Purchase #7 $128.88   12.216%   $144.624   $144.62   $144.60   $144.60  
  7 purchase totals = $868.97       $955.4383   $955.43   $955.40   $955.30