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	$37.94	12.137%	$42.5448	$42.54	$42.55	$42.50
Purchase #2	$88.82	12.814%	$100.2014	$100.20	$100.20	$100.20
Purchase #3	$197.42	11.146%	$219.4244	$219.42	$219.40	$219.40
Purchase #4	$111.64	4.334%	$116.4785	$116.48	$116.50	$116.50
Purchase #5	$165.59	13.253%	$187.5356	$187.54	$187.55	$187.50
Purchase #6	$22.25	3.748%	$23.0839	$23.08	$23.10	$23.10
Purchase #7	$111.63	7.494%	$119.9956	$120.00	$120.00	$120.00
7 purchase totals =	$735.29		$809.2642	$809.26	$809.30	$809.20