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	$40.97	8.577%	$44.484	$44.48	$44.50	$44.50
Purchase #2	$236.56	7.302%	$253.8336	$253.83	$253.85	$253.80
Purchase #3	$53.86	4.211%	$56.128	$56.13	$56.15	$56.10
Purchase #4	$179.81	8.425%	$194.959	$194.96	$194.95	$195.00
Purchase #5	$53.66	4.647%	$56.1536	$56.15	$56.15	$56.20
Purchase #6	$9.44	7.271%	$10.1264	$10.13	$10.15	$10.10
Purchase #7	$45.74	12.785%	$51.5879	$51.59	$51.60	$51.60
7 purchase totals =	$620.04		$667.2725	$667.27	$667.35	$667.30