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 $67.87   12.583%   $76.4101   $76.41   $76.40   $76.40  
  Purchase #2 $184.99   9.865%   $203.2393   $203.24   $203.25   $203.20  
  Purchase #3 $61.42   11.205%   $68.3021   $68.30   $68.30   $68.30  
  Purchase #4 $160.61   8.248%   $173.8571   $173.86   $173.85   $173.90  
  Purchase #5 $232.60   12.860%   $262.5124   $262.51   $262.50   $262.50  
  Purchase #6 $30.92   12.464%   $34.7739   $34.77   $34.75   $34.80  
  Purchase #7 $245.90   3.769%   $255.168   $255.17   $255.15   $255.20  
  7 purchase totals = $984.31       $1,074.2629   $1,074.26   $1,074.20   $1,074.30