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	$91.39	10.284%	$100.7885	$100.79	$100.80	$100.80
Purchase #2	$237.63	8.124%	$256.9351	$256.94	$256.95	$256.90
Purchase #3	$41.27	12.114%	$46.2694	$46.27	$46.25	$46.30
Purchase #4	$17.78	7.474%	$19.1089	$19.11	$19.10	$19.10
Purchase #5	$12.86	6.401%	$13.6832	$13.68	$13.70	$13.70
Purchase #6	$41.50	5.581%	$43.8161	$43.82	$43.80	$43.80
Purchase #7	$17.78	13.463%	$20.1737	$20.17	$20.15	$20.20
7 purchase totals =	$460.21		$500.7749	$500.78	$500.75	$500.80