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 $194.98   7.509%   $209.621   $209.62   $209.60   $209.60  
  Purchase #2 $136.43   3.751%   $141.5475   $141.55   $141.55   $141.50  
  Purchase #3 $8.97   3.475%   $9.2817   $9.28   $9.30   $9.30  
  Purchase #4 $111.36   4.454%   $116.32   $116.32   $116.30   $116.30  
  Purchase #5 $236.73   8.230%   $256.2129   $256.21   $256.20   $256.20  
  Purchase #6 $24.59   7.255%   $26.374   $26.37   $26.35   $26.40  
  Purchase #7 $191.89   12.863%   $216.5728   $216.57   $216.55   $216.60  
  7 purchase totals = $904.95       $975.9299   $975.92   $975.85   $975.90