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 $156.94   6.238%   $166.7299   $166.73   $166.75   $166.70  
  Purchase #2 $249.61   4.628%   $261.162   $261.16   $261.15   $261.20  
  Purchase #3 $220.43   11.725%   $246.2754   $246.28   $246.30   $246.30  
  Purchase #4 $246.37   7.769%   $265.5105   $265.51   $265.50   $265.50  
  Purchase #5 $171.67   6.235%   $182.3736   $182.37   $182.35   $182.40  
  Purchase #6 $131.97   12.439%   $148.3857   $148.39   $148.40   $148.40  
  Purchase #7 $156.89   3.281%   $162.0376   $162.04   $162.05   $162.00  
  7 purchase totals = $1,333.88       $1,432.4747   $1,432.48   $1,432.50   $1,432.50