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 $138.98   5.577%   $146.7309   $146.73   $146.75   $146.70  
  Purchase #2 $207.64   4.181%   $216.3214   $216.32   $216.30   $216.30  
  Purchase #3 $108.73   3.451%   $112.4823   $112.48   $112.50   $112.50  
  Purchase #4 $245.85   6.591%   $262.054   $262.05   $262.05   $262.10  
  Purchase #5 $203.68   10.141%   $224.3352   $224.34   $224.35   $224.30  
  Purchase #6 $67.33   13.822%   $76.6364   $76.64   $76.65   $76.60  
  Purchase #7 $157.32   10.605%   $174.0038   $174.00   $174.00   $174.00  
  7 purchase totals = $1,129.53       $1,212.5640   $1,212.56   $1,212.60   $1,212.50