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	$46.47	10.539%	$51.3675	$51.37	$51.35	$51.40
Purchase #2	$131.80	13.408%	$149.4717	$149.47	$149.45	$149.50
Purchase #3	$128.31	4.733%	$134.3829	$134.38	$134.40	$134.40
Purchase #4	$156.32	10.446%	$172.6492	$172.65	$172.65	$172.60
Purchase #5	$96.41	9.811%	$105.8688	$105.87	$105.85	$105.90
Purchase #6	$27.87	3.759%	$28.9176	$28.92	$28.90	$28.90
Purchase #7	$164.27	11.784%	$183.6276	$183.63	$183.65	$183.60
7 purchase totals =	$751.45		$826.2853	$826.29	$826.25	$826.30