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	$84.43	6.845%	$90.2092	$90.21	$90.20	$90.20
Purchase #2	$125.79	6.233%	$133.6305	$133.63	$133.65	$133.60
Purchase #3	$53.93	10.510%	$59.598	$59.60	$59.60	$59.60
Purchase #4	$77.93	12.642%	$87.7819	$87.78	$87.80	$87.80
Purchase #5	$114.88	11.213%	$127.7615	$127.76	$127.75	$127.80
Purchase #6	$33.33	11.587%	$37.1919	$37.19	$37.20	$37.20
Purchase #7	$181.97	5.614%	$192.1858	$192.19	$192.20	$192.20
7 purchase totals =	$672.26		$728.3588	$728.36	$728.40	$728.40