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	$30.34	6.478%	$32.3054	$32.31	$32.30	$32.30
Purchase #2	$159.25	6.823%	$170.1156	$170.12	$170.10	$170.10
Purchase #3	$43.63	9.464%	$47.7591	$47.76	$47.75	$47.80
Purchase #4	$143.54	7.853%	$154.8122	$154.81	$154.80	$154.80
Purchase #5	$48.40	12.421%	$54.4118	$54.41	$54.40	$54.40
Purchase #6	$19.40	5.310%	$20.4301	$20.43	$20.45	$20.40
Purchase #7	$39.39	9.217%	$43.0206	$43.02	$43.00	$43.00
7 purchase totals =	$483.95		$522.8548	$522.86	$522.80	$522.80