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 $68.53   4.591%   $71.6762   $71.68   $71.70   $71.70  
  Purchase #2 $171.44   10.848%   $190.0378   $190.04   $190.05   $190.00  
  Purchase #3 $37.26   7.102%   $39.9062   $39.91   $39.90   $39.90  
  Purchase #4 $24.27   5.367%   $25.5726   $25.57   $25.55   $25.60  
  Purchase #5 $229.42   8.102%   $248.0076   $248.01   $248.00   $248.00  
  Purchase #6 $250.99   10.766%   $278.0116   $278.01   $278.00   $278.00  
  Purchase #7 $204.85   5.571%   $216.2622   $216.26   $216.25   $216.30  
  7 purchase totals = $986.76       $1,069.4742   $1,069.48   $1,069.45   $1,069.50