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 $162.63   8.249%   $176.0453   $176.05   $176.05   $176.00  
  Purchase #2 $29.59   7.868%   $31.9181   $31.92   $31.90   $31.90  
  Purchase #3 $226.35   9.790%   $248.5097   $248.51   $248.50   $248.50  
  Purchase #4 $248.59   7.321%   $266.7893   $266.79   $266.80   $266.80  
  Purchase #5 $7.96   9.517%   $8.7176   $8.72   $8.70   $8.70  
  Purchase #6 $223.58   4.219%   $233.0128   $233.01   $233.00   $233.00  
  Purchase #7 $207.72   13.752%   $236.2857   $236.29   $236.30   $236.30  
  7 purchase totals = $1,106.42       $1,201.2785   $1,201.29   $1,201.25   $1,201.20