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	$10.25	6.451%	$10.9112	$10.91	$10.90	$10.90
Purchase #2	$97.39	5.718%	$102.9588	$102.96	$102.95	$103.00
Purchase #3	$229.72	12.525%	$258.4924	$258.49	$258.50	$258.50
Purchase #4	$129.40	11.573%	$144.3755	$144.38	$144.40	$144.40
Purchase #5	$127.26	4.416%	$132.8798	$132.88	$132.90	$132.90
Purchase #6	$243.89	10.660%	$269.8887	$269.89	$269.90	$269.90
Purchase #7	$160.61	7.347%	$172.41	$172.41	$172.40	$172.40
7 purchase totals =	$998.52		$1,091.9164	$1,091.92	$1,091.95	$1,092.00