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	$82.31	8.719%	$89.4866	$89.49	$89.50	$89.50
Purchase #2	$12.82	5.143%	$13.4793	$13.48	$13.50	$13.50
Purchase #3	$207.27	12.727%	$233.6493	$233.65	$233.65	$233.60
Purchase #4	$223.62	8.783%	$243.2605	$243.26	$243.25	$243.30
Purchase #5	$92.28	10.500%	$101.9694	$101.97	$101.95	$102.00
Purchase #6	$63.50	10.500%	$70.1675	$70.17	$70.15	$70.20
Purchase #7	$58.52	7.487%	$62.9014	$62.90	$62.90	$62.90
7 purchase totals =	$740.32		$814.9140	$814.92	$814.90	$815.00