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	$21.56	6.344%	$22.9278	$22.93	$22.95	$22.90
Purchase #2	$42.64	9.289%	$46.6008	$46.60	$46.60	$46.60
Purchase #3	$166.79	13.258%	$188.903	$188.90	$188.90	$188.90
Purchase #4	$55.70	10.356%	$61.4683	$61.47	$61.45	$61.50
Purchase #5	$37.82	13.201%	$42.8126	$42.81	$42.80	$42.80
Purchase #6	$139.46	11.249%	$155.1479	$155.15	$155.15	$155.10
Purchase #7	$174.78	12.299%	$196.2762	$196.28	$196.30	$196.30
7 purchase totals =	$638.75		$714.1366	$714.14	$714.15	$714.10