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	$82.65	7.412%	$88.776	$88.78	$88.80	$88.80
Purchase #2	$98.87	6.328%	$105.1265	$105.13	$105.15	$105.10
Purchase #3	$35.99	7.230%	$38.5921	$38.59	$38.60	$38.60
Purchase #4	$48.78	9.677%	$53.5004	$53.50	$53.50	$53.50
Purchase #5	$19.61	10.470%	$21.6632	$21.66	$21.65	$21.70
Purchase #6	$87.25	4.771%	$91.4127	$91.41	$91.40	$91.40
Purchase #7	$95.50	9.585%	$104.6537	$104.65	$104.65	$104.70
7 purchase totals =	$468.65		$503.7246	$503.72	$503.75	$503.80