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	$50.91	6.145%	$54.0384	$54.04	$54.05	$54.00
Purchase #2	$150.42	8.341%	$162.9665	$162.97	$162.95	$163.00
Purchase #3	$179.26	10.547%	$198.1666	$198.17	$198.15	$198.20
Purchase #4	$131.54	8.243%	$142.3828	$142.38	$142.40	$142.40
Purchase #5	$146.69	4.795%	$153.7238	$153.72	$153.70	$153.70
Purchase #6	$18.38	9.360%	$20.1004	$20.10	$20.10	$20.10
Purchase #7	$111.92	7.613%	$120.4405	$120.44	$120.45	$120.40
7 purchase totals =	$789.12		$851.8190	$851.82	$851.80	$851.80