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 $163.55   12.622%   $184.1933   $184.19   $184.20   $184.20  
  Purchase #2 $219.37   8.337%   $237.6589   $237.66   $237.65   $237.70  
  Purchase #3 $60.64   10.559%   $67.043   $67.04   $67.05   $67.00  
  Purchase #4 $197.50   9.177%   $215.6246   $215.62   $215.60   $215.60  
  Purchase #5 $228.47   5.466%   $240.9582   $240.96   $240.95   $241.00  
  Purchase #6 $124.85   8.571%   $135.5509   $135.55   $135.55   $135.60  
  Purchase #7 $13.66   13.401%   $15.4906   $15.49   $15.50   $15.50  
  7 purchase totals = $1,008.04       $1,096.5195   $1,096.51   $1,096.50   $1,096.60