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	$38.33	12.376%	$43.0737	$43.07	$43.05	$43.10
Purchase #2	$105.50	11.778%	$117.9258	$117.93	$117.95	$117.90
Purchase #3	$245.61	13.358%	$278.4186	$278.42	$278.40	$278.40
Purchase #4	$72.70	10.750%	$80.5153	$80.52	$80.50	$80.50
Purchase #5	$5.39	13.834%	$6.1357	$6.14	$6.15	$6.10
Purchase #6	$107.87	6.146%	$114.4997	$114.50	$114.50	$114.50
Purchase #7	$127.54	13.502%	$144.7605	$144.76	$144.75	$144.80
7 purchase totals =	$702.94		$785.3293	$785.34	$785.30	$785.30