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	$103.51	8.104%	$111.8985	$111.90	$111.90	$111.90
Purchase #2	$137.72	8.425%	$149.3229	$149.32	$149.30	$149.30
Purchase #3	$179.91	8.121%	$194.5205	$194.52	$194.50	$194.50
Purchase #4	$248.81	12.351%	$279.5405	$279.54	$279.55	$279.50
Purchase #5	$191.54	9.166%	$209.0966	$209.10	$209.10	$209.10
Purchase #6	$130.43	10.130%	$143.6426	$143.64	$143.65	$143.60
Purchase #7	$24.56	5.437%	$25.8953	$25.90	$25.90	$25.90
7 purchase totals =	$1,016.48		$1,113.9169	$1,113.92	$1,113.90	$1,113.80