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	$241.72	13.211%	$273.6536	$273.65	$273.65	$273.70
Purchase #2	$135.54	5.338%	$142.7751	$142.78	$142.80	$142.80
Purchase #3	$84.45	5.245%	$88.8794	$88.88	$88.90	$88.90
Purchase #4	$54.86	8.383%	$59.4589	$59.46	$59.45	$59.50
Purchase #5	$103.34	7.839%	$111.4408	$111.44	$111.45	$111.40
Purchase #6	$11.64	9.347%	$12.728	$12.73	$12.75	$12.70
Purchase #7	$6.51	4.463%	$6.8005	$6.80	$6.80	$6.80
7 purchase totals =	$638.06		$695.7363	$695.74	$695.80	$695.80