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	$20.84	3.203%	$21.5075	$21.51	$21.50	$21.50
Purchase #2	$230.50	10.484%	$254.6656	$254.67	$254.65	$254.70
Purchase #3	$42.83	7.724%	$46.1382	$46.14	$46.15	$46.10
Purchase #4	$9.83	12.849%	$11.0931	$11.09	$11.10	$11.10
Purchase #5	$104.41	13.822%	$118.8416	$118.84	$118.85	$118.80
Purchase #6	$245.76	12.108%	$275.5166	$275.52	$275.50	$275.50
Purchase #7	$203.93	9.585%	$223.4767	$223.48	$223.50	$223.50
7 purchase totals =	$858.10		$951.2393	$951.25	$951.25	$951.20