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	$31.71	5.697%	$33.5165	$33.52	$33.50	$33.50
Purchase #2	$179.71	6.688%	$191.729	$191.73	$191.75	$191.70
Purchase #3	$194.39	11.147%	$216.0587	$216.06	$216.05	$216.10
Purchase #4	$89.40	11.455%	$99.6408	$99.64	$99.65	$99.60
Purchase #5	$113.25	12.203%	$127.0699	$127.07	$127.05	$127.10
Purchase #6	$183.60	9.831%	$201.6497	$201.65	$201.65	$201.60
Purchase #7	$248.84	13.170%	$281.6122	$281.61	$281.60	$281.60
7 purchase totals =	$1,040.90		$1,151.2768	$1,151.28	$1,151.25	$1,151.20