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	$223.94	12.290%	$251.4622	$251.46	$251.45	$251.50
Purchase #2	$250.34	8.372%	$271.2985	$271.30	$271.30	$271.30
Purchase #3	$144.33	5.834%	$152.7502	$152.75	$152.75	$152.80
Purchase #4	$26.31	4.156%	$27.4034	$27.40	$27.40	$27.40
Purchase #5	$114.93	4.826%	$120.4765	$120.48	$120.50	$120.50
Purchase #6	$127.46	11.780%	$142.4748	$142.47	$142.45	$142.50
Purchase #7	$104.69	13.419%	$118.7384	$118.74	$118.75	$118.70
7 purchase totals =	$992.00		$1,084.6040	$1,084.60	$1,084.60	$1,084.70