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	$205.66	12.113%	$230.5716	$230.57	$230.55	$230.60
Purchase #2	$187.86	8.808%	$204.4067	$204.41	$204.40	$204.40
Purchase #3	$82.32	8.146%	$89.0258	$89.03	$89.05	$89.00
Purchase #4	$145.55	4.710%	$152.4054	$152.41	$152.40	$152.40
Purchase #5	$53.88	10.742%	$59.6678	$59.67	$59.65	$59.70
Purchase #6	$154.83	3.129%	$159.6746	$159.67	$159.65	$159.70
Purchase #7	$89.36	6.293%	$94.9834	$94.98	$95.00	$95.00
7 purchase totals =	$919.46		$990.7353	$990.74	$990.70	$990.80