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	$84.98	5.210%	$89.4075	$89.41	$89.40	$89.40
Purchase #2	$74.73	4.745%	$78.2759	$78.28	$78.30	$78.30
Purchase #3	$40.33	5.371%	$42.4961	$42.50	$42.50	$42.50
Purchase #4	$88.86	3.111%	$91.6244	$91.62	$91.60	$91.60
Purchase #5	$221.58	9.640%	$242.9403	$242.94	$242.95	$242.90
Purchase #6	$65.96	5.627%	$69.6716	$69.67	$69.65	$69.70
Purchase #7	$9.96	7.132%	$10.6703	$10.67	$10.65	$10.70
7 purchase totals =	$586.40		$625.0861	$625.09	$625.05	$625.10