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	$61.56	3.689%	$63.8309	$63.83	$63.85	$63.80
Purchase #2	$93.56	6.776%	$99.8996	$99.90	$99.90	$99.90
Purchase #3	$115.66	10.254%	$127.5198	$127.52	$127.50	$127.50
Purchase #4	$44.26	12.124%	$49.6261	$49.63	$49.65	$49.60
Purchase #5	$162.89	6.634%	$173.6961	$173.70	$173.70	$173.70
Purchase #6	$36.69	9.719%	$40.2559	$40.26	$40.25	$40.30
Purchase #7	$105.52	4.285%	$110.0415	$110.04	$110.05	$110.00
7 purchase totals =	$620.14		$664.8699	$664.88	$664.90	$664.80