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 $149.90   5.538%   $158.2015   $158.20   $158.20   $158.20  
  Purchase #2 $154.91   11.776%   $173.1522   $173.15   $173.15   $173.20  
  Purchase #3 $195.47   5.754%   $206.7173   $206.72   $206.70   $206.70  
  Purchase #4 $192.54   11.616%   $214.9054   $214.91   $214.90   $214.90  
  Purchase #5 $227.43   3.134%   $234.5577   $234.56   $234.55   $234.60  
  Purchase #6 $120.47   9.658%   $132.105   $132.11   $132.10   $132.10  
  Purchase #7 $26.77   11.548%   $29.8614   $29.86   $29.85   $29.90  
  7 purchase totals = $1,067.49       $1,149.5005   $1,149.51   $1,149.45   $1,149.60