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	$46.30	13.492%	$52.5468	$52.55	$52.55	$52.50
Purchase #2	$220.36	6.850%	$235.4547	$235.45	$235.45	$235.50
Purchase #3	$41.36	5.809%	$43.7626	$43.76	$43.75	$43.80
Purchase #4	$83.62	7.409%	$89.8154	$89.82	$89.80	$89.80
Purchase #5	$16.43	6.549%	$17.506	$17.51	$17.50	$17.50
Purchase #6	$57.78	5.658%	$61.0492	$61.05	$61.05	$61.00
Purchase #7	$134.46	8.222%	$145.5153	$145.52	$145.50	$145.50
7 purchase totals =	$600.31		$645.6500	$645.66	$645.60	$645.60