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	$89.66	11.671%	$100.1242	$100.12	$100.10	$100.10
Purchase #2	$59.40	8.797%	$64.6254	$64.63	$64.65	$64.60
Purchase #3	$233.87	8.410%	$253.5385	$253.54	$253.55	$253.50
Purchase #4	$215.26	12.152%	$241.4184	$241.42	$241.40	$241.40
Purchase #5	$101.67	11.633%	$113.4973	$113.50	$113.50	$113.50
Purchase #6	$241.38	8.500%	$261.8973	$261.90	$261.90	$261.90
Purchase #7	$58.30	7.546%	$62.6993	$62.70	$62.70	$62.70
7 purchase totals =	$999.54		$1,097.8004	$1,097.81	$1,097.80	$1,097.70