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	$113.48	8.407%	$123.0203	$123.02	$123.00	$123.00
Purchase #2	$61.83	9.733%	$67.8479	$67.85	$67.85	$67.80
Purchase #3	$105.74	12.354%	$118.8031	$118.80	$118.80	$118.80
Purchase #4	$148.81	5.345%	$156.7639	$156.76	$156.75	$156.80
Purchase #5	$130.81	6.810%	$139.7182	$139.72	$139.70	$139.70
Purchase #6	$177.82	9.240%	$194.2506	$194.25	$194.25	$194.30
Purchase #7	$61.98	10.419%	$68.4377	$68.44	$68.45	$68.40
7 purchase totals =	$800.47		$868.8417	$868.84	$868.80	$868.80