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	$192.37	6.204%	$204.3046	$204.30	$204.30	$204.30
Purchase #2	$249.88	4.288%	$260.5949	$260.59	$260.60	$260.60
Purchase #3	$44.63	11.697%	$49.8504	$49.85	$49.85	$49.90
Purchase #4	$119.94	13.708%	$136.3814	$136.38	$136.40	$136.40
Purchase #5	$57.30	5.152%	$60.2521	$60.25	$60.25	$60.30
Purchase #6	$81.41	9.501%	$89.1448	$89.14	$89.15	$89.10
Purchase #7	$100.43	11.281%	$111.7595	$111.76	$111.75	$111.80
7 purchase totals =	$845.96		$912.2877	$912.27	$912.30	$912.40