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	$188.91	9.691%	$207.2173	$207.22	$207.20	$207.20
Purchase #2	$96.91	6.478%	$103.1878	$103.19	$103.20	$103.20
Purchase #3	$176.76	13.289%	$200.2496	$200.25	$200.25	$200.20
Purchase #4	$250.91	9.769%	$275.4214	$275.42	$275.40	$275.40
Purchase #5	$132.81	6.753%	$141.7787	$141.78	$141.80	$141.80
Purchase #6	$132.48	8.738%	$144.0561	$144.06	$144.05	$144.10
Purchase #7	$24.81	11.259%	$27.6034	$27.60	$27.60	$27.60
7 purchase totals =	$1,003.59		$1,099.5143	$1,099.52	$1,099.50	$1,099.50