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	$19.78	5.497%	$20.8673	$20.87	$20.85	$20.90
Purchase #2	$176.49	7.525%	$189.7709	$189.77	$189.75	$189.80
Purchase #3	$69.60	12.724%	$78.4559	$78.46	$78.45	$78.50
Purchase #4	$142.91	11.360%	$159.1446	$159.14	$159.15	$159.10
Purchase #5	$72.89	3.237%	$75.2494	$75.25	$75.25	$75.20
Purchase #6	$174.50	9.110%	$190.397	$190.40	$190.40	$190.40
Purchase #7	$236.34	7.326%	$253.6543	$253.65	$253.65	$253.70
7 purchase totals =	$892.51		$967.5394	$967.54	$967.50	$967.60