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	$63.90	6.271%	$67.9072	$67.91	$67.90	$67.90
Purchase #2	$237.72	12.603%	$267.6799	$267.68	$267.70	$267.70
Purchase #3	$170.63	11.544%	$190.3275	$190.33	$190.35	$190.30
Purchase #4	$19.43	12.386%	$21.8366	$21.84	$21.85	$21.80
Purchase #5	$250.74	4.663%	$262.432	$262.43	$262.45	$262.40
Purchase #6	$56.76	10.631%	$62.7942	$62.79	$62.80	$62.80
Purchase #7	$206.87	9.788%	$227.1184	$227.12	$227.10	$227.10
7 purchase totals =	$1,006.05		$1,100.0958	$1,100.10	$1,100.15	$1,100.00