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	$46.49	7.768%	$50.1013	$50.10	$50.10	$50.10
Purchase #2	$231.76	5.290%	$244.0201	$244.02	$244.00	$244.00
Purchase #3	$18.33	11.535%	$20.4444	$20.44	$20.45	$20.40
Purchase #4	$114.96	11.171%	$127.8022	$127.80	$127.80	$127.80
Purchase #5	$164.72	3.121%	$169.8609	$169.86	$169.85	$169.90
Purchase #6	$181.69	7.204%	$194.7789	$194.78	$194.80	$194.80
Purchase #7	$237.75	4.288%	$247.9447	$247.94	$247.95	$247.90
7 purchase totals =	$995.70		$1,054.9525	$1,054.94	$1,054.95	$1,054.90