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	$167.48	12.784%	$188.8906	$188.89	$188.90	$188.90
Purchase #2	$157.39	5.457%	$165.9788	$165.98	$166.00	$166.00
Purchase #3	$38.95	12.254%	$43.7229	$43.72	$43.70	$43.70
Purchase #4	$121.31	6.296%	$128.9477	$128.95	$128.95	$128.90
Purchase #5	$101.91	3.163%	$105.1334	$105.13	$105.15	$105.10
Purchase #6	$72.65	10.358%	$80.1751	$80.18	$80.20	$80.20
Purchase #7	$58.53	10.399%	$64.6165	$64.62	$64.60	$64.60
7 purchase totals =	$718.22		$777.4650	$777.47	$777.50	$777.40