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	$205.73	3.733%	$213.4099	$213.41	$213.40	$213.40
Purchase #2	$180.86	9.656%	$198.3238	$198.32	$198.30	$198.30
Purchase #3	$145.69	9.578%	$159.6442	$159.64	$159.65	$159.60
Purchase #4	$195.38	10.600%	$216.0903	$216.09	$216.10	$216.10
Purchase #5	$217.34	3.803%	$225.6054	$225.61	$225.60	$225.60
Purchase #6	$86.27	5.642%	$91.1374	$91.14	$91.15	$91.10
Purchase #7	$18.59	3.185%	$19.1821	$19.18	$19.20	$19.20
7 purchase totals =	$1,049.86		$1,123.3931	$1,123.39	$1,123.40	$1,123.30