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	$210.29	13.637%	$238.9672	$238.97	$238.95	$239.00
Purchase #2	$40.31	3.864%	$41.8676	$41.87	$41.85	$41.90
Purchase #3	$116.76	11.804%	$130.5424	$130.54	$130.55	$130.50
Purchase #4	$187.56	3.170%	$193.5057	$193.51	$193.50	$193.50
Purchase #5	$80.38	13.489%	$91.2225	$91.22	$91.20	$91.20
Purchase #6	$47.60	13.711%	$54.1264	$54.13	$54.15	$54.10
Purchase #7	$55.60	6.260%	$59.0806	$59.08	$59.10	$59.10
7 purchase totals =	$738.50		$809.3124	$809.32	$809.30	$809.30