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 $186.64   6.211%   $198.2322   $198.23   $198.25   $198.20  
  Purchase #2 $209.85   12.543%   $236.1715   $236.17   $236.15   $236.20  
  Purchase #3 $194.43   5.162%   $204.4665   $204.47   $204.45   $204.50  
  Purchase #4 $84.64   12.281%   $95.0346   $95.03   $95.05   $95.00  
  Purchase #5 $175.35   11.191%   $194.9734   $194.97   $194.95   $195.00  
  Purchase #6 $192.33   9.779%   $211.138   $211.14   $211.15   $211.10  
  Purchase #7 $142.28   10.749%   $157.5737   $157.57   $157.55   $157.60  
  7 purchase totals = $1,185.52       $1,297.5899   $1,297.58   $1,297.55   $1,297.60