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 $248.68   8.250%   $269.1961   $269.20   $269.20   $269.20  
  Purchase #2 $69.88   4.848%   $73.2678   $73.27   $73.25   $73.30  
  Purchase #3 $41.99   13.258%   $47.557   $47.56   $47.55   $47.60  
  Purchase #4 $65.58   8.258%   $70.9956   $71.00   $71.00   $71.00  
  Purchase #5 $62.58   13.551%   $71.0602   $71.06   $71.05   $71.10  
  Purchase #6 $145.36   7.765%   $156.6472   $156.65   $156.65   $156.60  
  Purchase #7 $249.50   4.569%   $260.8997   $260.90   $260.90   $260.90  
  7 purchase totals = $883.57       $949.6236   $949.64   $949.60   $949.70