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 $87.51   10.491%   $96.6907   $96.69   $96.70   $96.70  
  Purchase #2 $181.31   4.574%   $189.6031   $189.60   $189.60   $189.60  
  Purchase #3 $215.58   5.329%   $227.0683   $227.07   $227.05   $227.10  
  Purchase #4 $69.44   9.661%   $76.1486   $76.15   $76.15   $76.10  
  Purchase #5 $115.44   7.569%   $124.1777   $124.18   $124.20   $124.20  
  Purchase #6 $140.80   6.171%   $149.4888   $149.49   $149.50   $149.50  
  Purchase #7 $128.57   8.597%   $139.6232   $139.62   $139.60   $139.60  
  7 purchase totals = $938.65       $1,002.8004   $1,002.80   $1,002.80   $1,002.80