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	$19.69	4.211%	$20.5191	$20.52	$20.50	$20.50
Purchase #2	$112.74	13.118%	$127.5292	$127.53	$127.55	$127.50
Purchase #3	$244.73	7.351%	$262.7201	$262.72	$262.70	$262.70
Purchase #4	$199.52	13.870%	$227.1934	$227.19	$227.20	$227.20
Purchase #5	$161.83	5.379%	$170.5348	$170.53	$170.55	$170.50
Purchase #6	$92.56	4.188%	$96.4364	$96.44	$96.45	$96.40
Purchase #7	$241.54	11.367%	$268.9959	$269.00	$269.00	$269.00
7 purchase totals =	$1,072.61		$1,173.9289	$1,173.93	$1,173.95	$1,173.80