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	$5.41	13.630%	$6.1474	$6.15	$6.15	$6.10
Purchase #2	$166.74	13.431%	$189.1348	$189.13	$189.15	$189.10
Purchase #3	$59.45	4.149%	$61.9166	$61.92	$61.90	$61.90
Purchase #4	$128.83	8.117%	$139.2871	$139.29	$139.30	$139.30
Purchase #5	$123.94	5.106%	$130.2684	$130.27	$130.25	$130.30
Purchase #6	$159.25	9.382%	$174.1908	$174.19	$174.20	$174.20
Purchase #7	$179.94	8.334%	$194.9362	$194.94	$194.95	$194.90
7 purchase totals =	$823.56		$895.8813	$895.89	$895.90	$895.80