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	$60.76	9.312%	$66.418	$66.42	$66.40	$66.40
Purchase #2	$15.87	12.196%	$17.8055	$17.81	$17.80	$17.80
Purchase #3	$209.79	13.815%	$238.7725	$238.77	$238.75	$238.80
Purchase #4	$53.33	12.298%	$59.8885	$59.89	$59.90	$59.90
Purchase #5	$143.40	4.130%	$149.3224	$149.32	$149.30	$149.30
Purchase #6	$30.93	9.271%	$33.7975	$33.80	$33.80	$33.80
Purchase #7	$142.39	4.541%	$148.8559	$148.86	$148.85	$148.90
7 purchase totals =	$656.47		$714.8603	$714.87	$714.80	$714.90