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	$32.35	11.689%	$36.1314	$36.13	$36.15	$36.10
Purchase #2	$72.29	12.675%	$81.4528	$81.45	$81.45	$81.50
Purchase #3	$99.32	11.229%	$110.4726	$110.47	$110.45	$110.50
Purchase #4	$77.56	13.465%	$88.0035	$88.00	$88.00	$88.00
Purchase #5	$57.96	6.106%	$61.499	$61.50	$61.50	$61.50
Purchase #6	$16.30	5.175%	$17.1435	$17.14	$17.15	$17.10
Purchase #7	$141.56	10.494%	$156.4153	$156.42	$156.40	$156.40
7 purchase totals =	$497.34		$551.1181	$551.11	$551.10	$551.10