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	$46.48	6.205%	$49.3641	$49.36	$49.35	$49.40
Purchase #2	$146.46	6.113%	$155.4131	$155.41	$155.40	$155.40
Purchase #3	$105.76	5.602%	$111.6847	$111.68	$111.70	$111.70
Purchase #4	$50.56	11.388%	$56.3178	$56.32	$56.30	$56.30
Purchase #5	$164.83	12.566%	$185.5425	$185.54	$185.55	$185.50
Purchase #6	$54.30	13.608%	$61.6891	$61.69	$61.70	$61.70
Purchase #7	$115.82	12.183%	$129.9304	$129.93	$129.95	$129.90
7 purchase totals =	$684.21		$749.9417	$749.93	$749.95	$749.90