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	$48.50	9.269%	$52.9955	$53.00	$53.00	$53.00
Purchase #2	$83.59	6.220%	$88.7893	$88.79	$88.80	$88.80
Purchase #3	$127.50	13.568%	$144.7992	$144.80	$144.80	$144.80
Purchase #4	$93.58	10.767%	$103.6558	$103.66	$103.65	$103.70
Purchase #5	$173.83	8.416%	$188.4595	$188.46	$188.45	$188.50
Purchase #6	$157.87	4.704%	$165.2962	$165.30	$165.30	$165.30
Purchase #7	$140.42	11.152%	$156.0796	$156.08	$156.10	$156.10
7 purchase totals =	$825.29		$900.0751	$900.09	$900.10	$900.20