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	$146.73	5.233%	$154.4084	$154.41	$154.40	$154.40
Purchase #2	$241.91	10.809%	$268.0581	$268.06	$268.05	$268.10
Purchase #3	$215.85	3.497%	$223.3983	$223.40	$223.40	$223.40
Purchase #4	$247.98	4.634%	$259.4714	$259.47	$259.45	$259.50
Purchase #5	$80.52	11.267%	$89.5922	$89.59	$89.60	$89.60
Purchase #6	$131.87	9.284%	$144.1128	$144.11	$144.10	$144.10
Purchase #7	$128.77	13.322%	$145.9247	$145.92	$145.90	$145.90
7 purchase totals =	$1,193.63		$1,284.9659	$1,284.96	$1,284.90	$1,285.00