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 $195.87   9.779%   $215.0241   $215.02   $215.00   $215.00  
  Purchase #2 $187.51   5.545%   $197.9074   $197.91   $197.90   $197.90  
  Purchase #3 $242.35   7.235%   $259.884   $259.88   $259.90   $259.90  
  Purchase #4 $92.74   3.153%   $95.6641   $95.66   $95.65   $95.70  
  Purchase #5 $239.28   5.638%   $252.7706   $252.77   $252.75   $252.80  
  Purchase #6 $152.39   13.216%   $172.5299   $172.53   $172.55   $172.50  
  Purchase #7 $73.41   10.197%   $80.8956   $80.90   $80.90   $80.90  
  7 purchase totals = $1,183.55       $1,274.6757   $1,274.67   $1,274.65   $1,274.70