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	$246.29	8.173%	$266.4193	$266.42	$266.40	$266.40
Purchase #2	$229.72	3.744%	$238.3207	$238.32	$238.30	$238.30
Purchase #3	$199.40	11.847%	$223.0229	$223.02	$223.00	$223.00
Purchase #4	$71.34	6.150%	$75.7274	$75.73	$75.75	$75.70
Purchase #5	$128.38	12.558%	$144.502	$144.50	$144.50	$144.50
Purchase #6	$49.72	5.687%	$52.5476	$52.55	$52.55	$52.50
Purchase #7	$52.68	6.501%	$56.1047	$56.10	$56.10	$56.10
7 purchase totals =	$977.53		$1,056.6446	$1,056.64	$1,056.60	$1,056.50