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	$7.43	11.706%	$8.2998	$8.30	$8.30	$8.30
Purchase #2	$10.33	7.450%	$11.0996	$11.10	$11.10	$11.10
Purchase #3	$40.50	5.168%	$42.593	$42.59	$42.60	$42.60
Purchase #4	$98.99	6.599%	$105.5224	$105.52	$105.50	$105.50
Purchase #5	$170.39	3.724%	$176.7353	$176.74	$176.75	$176.70
Purchase #6	$34.38	10.689%	$38.0549	$38.05	$38.05	$38.10
Purchase #7	$223.94	10.512%	$247.4806	$247.48	$247.50	$247.50
7 purchase totals =	$585.96		$629.7856	$629.78	$629.80	$629.80