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	$243.32	10.786%	$269.5645	$269.56	$269.55	$269.60
Purchase #2	$30.62	5.675%	$32.3577	$32.36	$32.35	$32.40
Purchase #3	$180.50	3.293%	$186.4439	$186.44	$186.45	$186.40
Purchase #4	$166.42	11.145%	$184.9675	$184.97	$184.95	$185.00
Purchase #5	$29.78	8.192%	$32.2196	$32.22	$32.20	$32.20
Purchase #6	$77.32	6.164%	$82.086	$82.09	$82.10	$82.10
Purchase #7	$127.56	4.493%	$133.2913	$133.29	$133.30	$133.30
7 purchase totals =	$855.52		$920.9305	$920.93	$920.90	$921.00