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	$79.89	13.169%	$90.4107	$90.41	$90.40	$90.40
Purchase #2	$59.94	9.697%	$65.7524	$65.75	$65.75	$65.80
Purchase #3	$180.27	8.338%	$195.3009	$195.30	$195.30	$195.30
Purchase #4	$14.46	11.298%	$16.0937	$16.09	$16.10	$16.10
Purchase #5	$164.64	8.395%	$178.4615	$178.46	$178.45	$178.50
Purchase #6	$100.64	4.843%	$105.514	$105.51	$105.50	$105.50
Purchase #7	$64.75	9.464%	$70.8779	$70.88	$70.90	$70.90
7 purchase totals =	$664.59		$722.4111	$722.40	$722.40	$722.50