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 $67.68   8.616%   $73.5113   $73.51   $73.50   $73.50  
  Purchase #2 $227.28   10.141%   $250.3285   $250.33   $250.35   $250.30  
  Purchase #3 $208.52   8.671%   $226.6008   $226.60   $226.60   $226.60  
  Purchase #4 $210.53   10.318%   $232.2525   $232.25   $232.25   $232.30  
  Purchase #5 $95.64   3.303%   $98.799   $98.80   $98.80   $98.80  
  Purchase #6 $241.77   12.291%   $271.486   $271.49   $271.50   $271.50  
  Purchase #7 $87.50   13.128%   $98.987   $98.99   $99.00   $99.00  
  7 purchase totals = $1,138.92       $1,251.9651   $1,251.97   $1,252.00   $1,252.00