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	$91.44	8.730%	$99.4227	$99.42	$99.40	$99.40
Purchase #2	$150.38	5.599%	$158.7998	$158.80	$158.80	$158.80
Purchase #3	$112.69	9.271%	$123.1375	$123.14	$123.15	$123.10
Purchase #4	$219.27	11.851%	$245.2557	$245.26	$245.25	$245.30
Purchase #5	$18.93	6.781%	$20.2136	$20.21	$20.20	$20.20
Purchase #6	$14.56	6.490%	$15.5049	$15.50	$15.50	$15.50
Purchase #7	$108.67	13.613%	$123.4632	$123.46	$123.45	$123.50
7 purchase totals =	$715.94		$785.7974	$785.79	$785.75	$785.80