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	$106.83	7.710%	$115.0666	$115.07	$115.05	$115.10
Purchase #2	$208.58	12.300%	$234.2353	$234.24	$234.25	$234.20
Purchase #3	$112.40	13.544%	$127.6235	$127.62	$127.60	$127.60
Purchase #4	$159.85	7.798%	$172.3151	$172.32	$172.30	$172.30
Purchase #5	$204.42	8.785%	$222.3783	$222.38	$222.40	$222.40
Purchase #6	$231.99	10.593%	$256.5647	$256.56	$256.55	$256.60
Purchase #7	$160.59	6.762%	$171.4491	$171.45	$171.45	$171.40
7 purchase totals =	$1,184.66		$1,299.6326	$1,299.64	$1,299.60	$1,299.60