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 $126.80   10.621%   $140.2674   $140.27   $140.25   $140.30  
  Purchase #2 $130.49   13.307%   $147.8543   $147.85   $147.85   $147.90  
  Purchase #3 $250.90   6.696%   $267.7003   $267.70   $267.70   $267.70  
  Purchase #4 $249.64   3.426%   $258.1927   $258.19   $258.20   $258.20  
  Purchase #5 $8.73   13.367%   $9.8969   $9.90   $9.90   $9.90  
  Purchase #6 $196.72   9.175%   $214.7691   $214.77   $214.75   $214.80  
  Purchase #7 $212.91   11.804%   $238.0419   $238.04   $238.05   $238.00  
  7 purchase totals = $1,176.19       $1,276.7226   $1,276.72   $1,276.70   $1,276.80