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	$226.53	11.737%	$253.1178	$253.12	$253.10	$253.10
Purchase #2	$181.94	3.267%	$187.884	$187.88	$187.90	$187.90
Purchase #3	$10.88	3.156%	$11.2234	$11.22	$11.20	$11.20
Purchase #4	$50.78	10.802%	$56.2653	$56.27	$56.25	$56.30
Purchase #5	$79.38	13.188%	$89.8486	$89.85	$89.85	$89.80
Purchase #6	$54.58	9.195%	$59.5986	$59.60	$59.60	$59.60
Purchase #7	$38.98	3.477%	$40.3353	$40.34	$40.35	$40.30
7 purchase totals =	$643.07		$698.2730	$698.28	$698.25	$698.20