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	$109.34	13.308%	$123.891	$123.89	$123.90	$123.90
Purchase #2	$165.52	7.444%	$177.8413	$177.84	$177.85	$177.80
Purchase #3	$74.93	5.820%	$79.2909	$79.29	$79.30	$79.30
Purchase #4	$190.75	10.818%	$211.3853	$211.39	$211.40	$211.40
Purchase #5	$115.83	6.639%	$123.52	$123.52	$123.50	$123.50
Purchase #6	$159.90	3.237%	$165.076	$165.08	$165.10	$165.10
Purchase #7	$120.59	9.588%	$132.1522	$132.15	$132.15	$132.20
7 purchase totals =	$936.86		$1,013.1567	$1,013.16	$1,013.20	$1,013.20