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	$80.78	5.848%	$85.504	$85.50	$85.50	$85.50
Purchase #2	$52.30	13.527%	$59.3746	$59.37	$59.35	$59.40
Purchase #3	$99.78	6.693%	$106.4583	$106.46	$106.45	$106.50
Purchase #4	$74.34	5.762%	$78.6235	$78.62	$78.60	$78.60
Purchase #5	$106.54	3.736%	$110.5203	$110.52	$110.50	$110.50
Purchase #6	$199.76	10.185%	$220.1056	$220.11	$220.10	$220.10
Purchase #7	$11.69	11.214%	$13.0009	$13.00	$13.00	$13.00
7 purchase totals =	$625.19		$673.5872	$673.58	$673.50	$673.60