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 $23.63   4.463%   $24.6846   $24.68   $24.70   $24.70  
  Purchase #2 $228.99   12.165%   $256.8466   $256.85   $256.85   $256.80  
  Purchase #3 $209.60   11.546%   $233.8004   $233.80   $233.80   $233.80  
  Purchase #4 $175.95   9.785%   $193.1667   $193.17   $193.15   $193.20  
  Purchase #5 $227.99   5.864%   $241.3593   $241.36   $241.35   $241.40  
  Purchase #6 $47.93   4.853%   $50.256   $50.26   $50.25   $50.30  
  Purchase #7 $174.86   4.691%   $183.0627   $183.06   $183.05   $183.10  
  7 purchase totals = $1,088.95       $1,183.1763   $1,183.18   $1,183.15   $1,183.30