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	$42.50	3.169%	$43.8468	$43.85	$43.85	$43.80
Purchase #2	$111.58	9.584%	$122.2738	$122.27	$122.25	$122.30
Purchase #3	$187.25	13.180%	$211.9296	$211.93	$211.95	$211.90
Purchase #4	$193.69	7.464%	$208.147	$208.15	$208.15	$208.10
Purchase #5	$56.83	12.793%	$64.1003	$64.10	$64.10	$64.10
Purchase #6	$91.37	3.857%	$94.8941	$94.89	$94.90	$94.90
Purchase #7	$84.74	11.619%	$94.5859	$94.59	$94.60	$94.60
7 purchase totals =	$767.96		$839.7775	$839.78	$839.80	$839.70