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	$103.49	13.485%	$117.4456	$117.45	$117.45	$117.40
Purchase #2	$145.31	7.281%	$155.89	$155.89	$155.90	$155.90
Purchase #3	$40.59	11.172%	$45.1247	$45.12	$45.10	$45.10
Purchase #4	$159.52	10.169%	$175.7416	$175.74	$175.75	$175.70
Purchase #5	$159.72	10.811%	$176.9873	$176.99	$177.00	$177.00
Purchase #6	$227.37	10.298%	$250.7846	$250.78	$250.80	$250.80
Purchase #7	$18.93	7.865%	$20.4188	$20.42	$20.40	$20.40
7 purchase totals =	$854.93		$942.3926	$942.39	$942.40	$942.30