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	$27.72	8.271%	$30.0127	$30.01	$30.00	$30.00
Purchase #2	$191.46	10.338%	$211.2531	$211.25	$211.25	$211.30
Purchase #3	$34.86	7.344%	$37.4201	$37.42	$37.40	$37.40
Purchase #4	$66.38	4.355%	$69.2708	$69.27	$69.25	$69.30
Purchase #5	$127.33	13.578%	$144.6189	$144.62	$144.60	$144.60
Purchase #6	$146.82	6.614%	$156.5307	$156.53	$156.55	$156.50
Purchase #7	$132.56	11.370%	$147.6321	$147.63	$147.65	$147.60
7 purchase totals =	$727.13		$796.7384	$796.73	$796.70	$796.70