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 $119.83   3.702%   $124.2661   $124.27   $124.25   $124.30  
  Purchase #2 $132.34   11.424%   $147.4585   $147.46   $147.45   $147.50  
  Purchase #3 $86.28   9.419%   $94.4067   $94.41   $94.40   $94.40  
  Purchase #4 $220.85   5.867%   $233.8073   $233.81   $233.80   $233.80  
  Purchase #5 $86.50   13.586%   $98.2519   $98.25   $98.25   $98.30  
  Purchase #6 $33.44   7.376%   $35.9065   $35.91   $35.90   $35.90  
  Purchase #7 $22.49   7.149%   $24.0978   $24.10   $24.10   $24.10  
  7 purchase totals = $701.73       $758.1948   $758.21   $758.15   $758.30