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	$154.89	9.202%	$169.143	$169.14	$169.15	$169.10
Purchase #2	$249.75	12.255%	$280.3569	$280.36	$280.35	$280.40
Purchase #3	$159.39	8.683%	$173.2298	$173.23	$173.25	$173.20
Purchase #4	$249.54	9.565%	$273.4085	$273.41	$273.40	$273.40
Purchase #5	$83.47	7.651%	$89.8563	$89.86	$89.85	$89.90
Purchase #6	$153.49	9.119%	$167.4868	$167.49	$167.50	$167.50
Purchase #7	$15.93	10.743%	$17.6414	$17.64	$17.65	$17.60
7 purchase totals =	$1,066.46		$1,171.1227	$1,171.13	$1,171.15	$1,171.10