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	$157.76	5.724%	$166.7902	$166.79	$166.80	$166.80
Purchase #2	$73.27	10.195%	$80.7399	$80.74	$80.75	$80.70
Purchase #3	$210.43	6.405%	$223.908	$223.91	$223.90	$223.90
Purchase #4	$80.31	11.635%	$89.6541	$89.65	$89.65	$89.70
Purchase #5	$147.25	7.700%	$158.5883	$158.59	$158.60	$158.60
Purchase #6	$17.60	10.381%	$19.4271	$19.43	$19.45	$19.40
Purchase #7	$241.85	13.611%	$274.7682	$274.77	$274.75	$274.80
7 purchase totals =	$928.47		$1,013.8758	$1,013.88	$1,013.90	$1,013.90