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 $156.83   12.412%   $176.2957   $176.30   $176.30   $176.30  
  Purchase #2 $71.49   7.480%   $76.8375   $76.84   $76.85   $76.80  
  Purchase #3 $204.81   6.847%   $218.8333   $218.83   $218.85   $218.80  
  Purchase #4 $230.63   10.348%   $254.4956   $254.50   $254.50   $254.50  
  Purchase #5 $136.88   6.179%   $145.3378   $145.34   $145.35   $145.30  
  Purchase #6 $219.64   8.135%   $237.5077   $237.51   $237.50   $237.50  
  Purchase #7 $83.96   3.537%   $86.9297   $86.93   $86.95   $86.90  
  7 purchase totals = $1,104.24       $1,196.2373   $1,196.25   $1,196.30   $1,196.10