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	$82.32	8.623%	$89.4185	$89.42	$89.40	$89.40
Purchase #2	$37.45	6.239%	$39.7865	$39.79	$39.80	$39.80
Purchase #3	$197.46	5.148%	$207.6252	$207.63	$207.65	$207.60
Purchase #4	$240.44	6.464%	$255.982	$255.98	$256.00	$256.00
Purchase #5	$136.38	5.431%	$143.7868	$143.79	$143.80	$143.80
Purchase #6	$123.87	3.107%	$127.7186	$127.72	$127.70	$127.70
Purchase #7	$38.28	13.398%	$43.4088	$43.41	$43.40	$43.40
7 purchase totals =	$856.20		$907.7264	$907.74	$907.75	$907.70