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	$102.33	11.404%	$113.9997	$114.00	$114.00	$114.00
Purchase #2	$72.46	10.602%	$80.1422	$80.14	$80.15	$80.10
Purchase #3	$212.55	4.426%	$221.9575	$221.96	$221.95	$222.00
Purchase #4	$139.95	13.355%	$158.6403	$158.64	$158.65	$158.60
Purchase #5	$23.56	5.770%	$24.9194	$24.92	$24.90	$24.90
Purchase #6	$94.92	10.480%	$104.8676	$104.87	$104.85	$104.90
Purchase #7	$107.48	3.592%	$111.3407	$111.34	$111.35	$111.30
7 purchase totals =	$753.25		$815.8674	$815.87	$815.85	$815.80