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	$246.56	11.692%	$275.3878	$275.39	$275.40	$275.40
Purchase #2	$52.44	12.658%	$59.0779	$59.08	$59.10	$59.10
Purchase #3	$163.59	5.857%	$173.1715	$173.17	$173.15	$173.20
Purchase #4	$23.90	13.386%	$27.0993	$27.10	$27.10	$27.10
Purchase #5	$144.87	6.341%	$154.0562	$154.06	$154.05	$154.10
Purchase #6	$67.54	3.685%	$70.0288	$70.03	$70.05	$70.00
Purchase #7	$33.73	12.451%	$37.9297	$37.93	$37.95	$37.90
7 purchase totals =	$732.63		$796.7512	$796.76	$796.80	$796.80