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 $177.41   10.239%   $195.575   $195.58   $195.60   $195.60  
  Purchase #2 $128.35   11.175%   $142.6931   $142.69   $142.70   $142.70  
  Purchase #3 $151.94   6.103%   $161.2129   $161.21   $161.20   $161.20  
  Purchase #4 $85.74   4.377%   $89.4928   $89.49   $89.50   $89.50  
  Purchase #5 $144.26   9.122%   $157.4194   $157.42   $157.40   $157.40  
  Purchase #6 $5.28   11.817%   $5.9039   $5.90   $5.90   $5.90  
  Purchase #7 $70.43   8.230%   $76.2264   $76.23   $76.25   $76.20  
  7 purchase totals = $763.41       $828.5235   $828.52   $828.55   $828.50