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	$95.38	5.434%	$100.5629	$100.56	$100.55	$100.60
Purchase #2	$41.96	11.131%	$46.6306	$46.63	$46.65	$46.60
Purchase #3	$76.89	3.807%	$79.8172	$79.82	$79.80	$79.80
Purchase #4	$186.43	11.366%	$207.6196	$207.62	$207.60	$207.60
Purchase #5	$140.48	9.546%	$153.8902	$153.89	$153.90	$153.90
Purchase #6	$236.54	13.624%	$268.7662	$268.77	$268.75	$268.80
Purchase #7	$32.54	4.219%	$33.9129	$33.91	$33.90	$33.90
7 purchase totals =	$810.22		$891.1996	$891.20	$891.15	$891.20