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 $100.37   4.126%   $104.5113   $104.51   $104.50   $104.50  
  Purchase #2 $246.97   4.714%   $258.6122   $258.61   $258.60   $258.60  
  Purchase #3 $115.80   4.728%   $121.275   $121.28   $121.30   $121.30  
  Purchase #4 $213.90   4.780%   $224.1244   $224.12   $224.10   $224.10  
  Purchase #5 $69.44   7.636%   $74.7424   $74.74   $74.75   $74.70  
  Purchase #6 $228.93   10.152%   $252.171   $252.17   $252.15   $252.20  
  Purchase #7 $215.76   4.836%   $226.1942   $226.19   $226.20   $226.20  
  7 purchase totals = $1,191.17       $1,261.6305   $1,261.62   $1,261.60   $1,261.60