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	$100.75	11.590%	$112.4269	$112.43	$112.45	$112.40
Purchase #2	$92.33	6.650%	$98.4699	$98.47	$98.45	$98.50
Purchase #3	$44.80	13.450%	$50.8256	$50.83	$50.85	$50.80
Purchase #4	$146.62	6.720%	$156.4729	$156.47	$156.45	$156.50
Purchase #5	$140.54	9.687%	$154.1541	$154.15	$154.15	$154.20
Purchase #6	$18.29	6.773%	$19.5288	$19.53	$19.55	$19.50
Purchase #7	$81.73	13.464%	$92.7341	$92.73	$92.75	$92.70
7 purchase totals =	$625.06		$684.6123	$684.61	$684.65	$684.60