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	$62.54	6.328%	$66.4975	$66.50	$66.50	$66.50
Purchase #2	$89.47	3.816%	$92.8842	$92.88	$92.90	$92.90
Purchase #3	$69.66	9.436%	$76.2331	$76.23	$76.25	$76.20
Purchase #4	$141.95	8.394%	$153.8653	$153.87	$153.85	$153.90
Purchase #5	$35.29	13.667%	$40.1131	$40.11	$40.10	$40.10
Purchase #6	$149.54	4.692%	$156.5564	$156.56	$156.55	$156.60
Purchase #7	$173.89	9.274%	$190.0166	$190.02	$190.00	$190.00
7 purchase totals =	$722.34		$776.1662	$776.17	$776.15	$776.20