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	$124.43	8.168%	$134.5934	$134.59	$134.60	$134.60
Purchase #2	$181.91	8.780%	$197.8817	$197.88	$197.90	$197.90
Purchase #3	$213.95	7.834%	$230.7108	$230.71	$230.70	$230.70
Purchase #4	$56.33	9.104%	$61.4583	$61.46	$61.45	$61.50
Purchase #5	$92.82	13.276%	$105.1428	$105.14	$105.15	$105.10
Purchase #6	$95.47	9.800%	$104.8261	$104.83	$104.85	$104.80
Purchase #7	$151.81	7.107%	$162.5991	$162.60	$162.60	$162.60
7 purchase totals =	$916.72		$997.2122	$997.21	$997.25	$997.20