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	$190.38	7.266%	$204.213	$204.21	$204.20	$204.20
Purchase #2	$64.83	11.618%	$72.3619	$72.36	$72.35	$72.40
Purchase #3	$189.60	5.370%	$199.7815	$199.78	$199.80	$199.80
Purchase #4	$80.38	12.711%	$90.5971	$90.60	$90.60	$90.60
Purchase #5	$17.43	3.500%	$18.0401	$18.04	$18.05	$18.00
Purchase #6	$126.93	13.842%	$144.4997	$144.50	$144.50	$144.50
Purchase #7	$230.91	4.354%	$240.9638	$240.96	$240.95	$241.00
7 purchase totals =	$900.46		$970.4571	$970.45	$970.45	$970.50