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	$39.30	3.354%	$40.6181	$40.62	$40.60	$40.60
Purchase #2	$72.98	5.358%	$76.8903	$76.89	$76.90	$76.90
Purchase #3	$56.92	10.203%	$62.7275	$62.73	$62.75	$62.70
Purchase #4	$162.39	10.565%	$179.5465	$179.55	$179.55	$179.50
Purchase #5	$141.46	12.149%	$158.646	$158.65	$158.65	$158.60
Purchase #6	$50.88	9.405%	$55.6653	$55.67	$55.65	$55.70
Purchase #7	$151.90	9.163%	$165.8186	$165.82	$165.80	$165.80
7 purchase totals =	$675.83		$739.9123	$739.93	$739.90	$739.80