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	$247.84	13.183%	$280.5127	$280.51	$280.50	$280.50
Purchase #2	$40.77	12.530%	$45.8785	$45.88	$45.90	$45.90
Purchase #3	$134.95	13.146%	$152.6905	$152.69	$152.70	$152.70
Purchase #4	$126.54	12.820%	$142.7624	$142.76	$142.75	$142.80
Purchase #5	$70.37	5.445%	$74.2016	$74.20	$74.20	$74.20
Purchase #6	$204.72	7.498%	$220.0699	$220.07	$220.05	$220.10
Purchase #7	$65.77	6.786%	$70.2332	$70.23	$70.25	$70.20
7 purchase totals =	$890.96		$986.3488	$986.34	$986.35	$986.40