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	$203.83	12.806%	$229.9325	$229.93	$229.95	$229.90
Purchase #2	$33.52	6.856%	$35.8181	$35.82	$35.80	$35.80
Purchase #3	$28.55	10.348%	$31.5044	$31.50	$31.50	$31.50
Purchase #4	$49.47	5.744%	$52.3116	$52.31	$52.30	$52.30
Purchase #5	$208.98	12.128%	$234.3251	$234.33	$234.35	$234.30
Purchase #6	$104.62	6.855%	$111.7917	$111.79	$111.80	$111.80
Purchase #7	$230.74	12.169%	$258.8188	$258.82	$258.80	$258.80
7 purchase totals =	$859.71		$954.5022	$954.50	$954.50	$954.40