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	$166.32	8.473%	$180.4123	$180.41	$180.40	$180.40
Purchase #2	$92.59	8.395%	$100.3629	$100.36	$100.35	$100.40
Purchase #3	$20.94	7.446%	$22.4992	$22.50	$22.50	$22.50
Purchase #4	$91.54	10.743%	$101.3741	$101.37	$101.35	$101.40
Purchase #5	$176.44	13.388%	$200.0618	$200.06	$200.05	$200.10
Purchase #6	$41.64	11.671%	$46.4998	$46.50	$46.50	$46.50
Purchase #7	$130.56	3.257%	$134.8123	$134.81	$134.80	$134.80
7 purchase totals =	$720.03		$786.0224	$786.01	$785.95	$786.10