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 $55.55   6.503%   $59.1624   $59.16   $59.15   $59.20  
  Purchase #2 $176.57   8.828%   $192.1576   $192.16   $192.15   $192.20  
  Purchase #3 $176.80   8.478%   $191.7891   $191.79   $191.80   $191.80  
  Purchase #4 $131.66   6.357%   $140.0296   $140.03   $140.05   $140.00  
  Purchase #5 $248.99   5.471%   $262.6122   $262.61   $262.60   $262.60  
  Purchase #6 $214.27   12.831%   $241.763   $241.76   $241.75   $241.80  
  Purchase #7 $225.77   13.392%   $256.0051   $256.01   $256.00   $256.00  
  7 purchase totals = $1,229.61       $1,343.5190   $1,343.52   $1,343.50   $1,343.60