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	$246.39	10.609%	$272.5295	$272.53	$272.55	$272.50
Purchase #2	$147.62	13.722%	$167.8764	$167.88	$167.90	$167.90
Purchase #3	$228.45	6.113%	$242.4151	$242.42	$242.40	$242.40
Purchase #4	$110.83	12.296%	$124.4577	$124.46	$124.45	$124.50
Purchase #5	$92.32	6.701%	$98.5064	$98.51	$98.50	$98.50
Purchase #6	$179.34	6.291%	$190.6223	$190.62	$190.60	$190.60
Purchase #7	$62.52	12.838%	$70.5463	$70.55	$70.55	$70.50
7 purchase totals =	$1,067.47		$1,166.9537	$1,166.97	$1,166.95	$1,166.90