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	$57.76	3.401%	$59.7244	$59.72	$59.70	$59.70
Purchase #2	$41.74	6.501%	$44.4535	$44.45	$44.45	$44.50
Purchase #3	$55.69	10.698%	$61.6477	$61.65	$61.65	$61.60
Purchase #4	$127.49	12.275%	$143.1394	$143.14	$143.15	$143.10
Purchase #5	$187.47	13.665%	$213.0878	$213.09	$213.10	$213.10
Purchase #6	$40.30	6.662%	$42.9848	$42.98	$43.00	$43.00
Purchase #7	$74.73	4.564%	$78.1407	$78.14	$78.15	$78.10
7 purchase totals =	$585.18		$643.1783	$643.17	$643.20	$643.10