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 $63.43   7.581%   $68.2386   $68.24   $68.25   $68.20  
  Purchase #2 $185.99   11.829%   $207.9908   $207.99   $208.00   $208.00  
  Purchase #3 $147.99   12.371%   $166.2978   $166.30   $166.30   $166.30  
  Purchase #4 $136.93   3.480%   $141.6952   $141.70   $141.70   $141.70  
  Purchase #5 $142.27   9.545%   $155.8497   $155.85   $155.85   $155.80  
  Purchase #6 $145.25   10.495%   $160.494   $160.49   $160.50   $160.50  
  Purchase #7 $101.82   12.698%   $114.7491   $114.75   $114.75   $114.70  
  7 purchase totals = $923.68       $1,015.3152   $1,015.32   $1,015.35   $1,015.20