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 $60.31   10.240%   $66.4857   $66.49   $66.50   $66.50  
  Purchase #2 $35.93   7.698%   $38.6959   $38.70   $38.70   $38.70  
  Purchase #3 $78.70   7.732%   $84.7851   $84.79   $84.80   $84.80  
  Purchase #4 $241.92   12.129%   $271.2625   $271.26   $271.25   $271.30  
  Purchase #5 $248.36   11.395%   $276.6606   $276.66   $276.65   $276.70  
  Purchase #6 $196.60   9.856%   $215.9769   $215.98   $216.00   $216.00  
  Purchase #7 $212.41   13.866%   $241.8628   $241.86   $241.85   $241.90  
  7 purchase totals = $1,074.23       $1,195.7295   $1,195.74   $1,195.75   $1,195.90