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	$25.79	5.573%	$27.2273	$27.23	$27.25	$27.20
Purchase #2	$100.94	6.572%	$107.5738	$107.57	$107.55	$107.60
Purchase #3	$220.62	13.503%	$250.4103	$250.41	$250.40	$250.40
Purchase #4	$82.29	9.138%	$89.8097	$89.81	$89.80	$89.80
Purchase #5	$134.72	10.103%	$148.3308	$148.33	$148.35	$148.30
Purchase #6	$130.64	7.643%	$140.6248	$140.62	$140.60	$140.60
Purchase #7	$35.45	5.387%	$37.3597	$37.36	$37.35	$37.40
7 purchase totals =	$730.45		$801.3364	$801.33	$801.30	$801.30