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	$55.40	3.262%	$57.2071	$57.21	$57.20	$57.20
Purchase #2	$10.72	13.707%	$12.1894	$12.19	$12.20	$12.20
Purchase #3	$29.89	4.156%	$31.1322	$31.13	$31.15	$31.10
Purchase #4	$52.30	6.284%	$55.5865	$55.59	$55.60	$55.60
Purchase #5	$76.83	5.114%	$80.7591	$80.76	$80.75	$80.80
Purchase #6	$39.26	11.817%	$43.8994	$43.90	$43.90	$43.90
Purchase #7	$173.58	7.661%	$186.878	$186.88	$186.90	$186.90
7 purchase totals =	$437.98		$467.6517	$467.66	$467.70	$467.70