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	$18.38	13.346%	$20.833	$20.83	$20.85	$20.80
Purchase #2	$128.60	12.414%	$144.5644	$144.56	$144.55	$144.60
Purchase #3	$154.41	4.716%	$161.692	$161.69	$161.70	$161.70
Purchase #4	$144.90	9.242%	$158.2917	$158.29	$158.30	$158.30
Purchase #5	$152.98	7.566%	$164.5545	$164.55	$164.55	$164.60
Purchase #6	$131.96	7.102%	$141.3318	$141.33	$141.35	$141.30
Purchase #7	$218.97	10.731%	$242.4677	$242.47	$242.45	$242.50
7 purchase totals =	$950.20		$1,033.7351	$1,033.72	$1,033.75	$1,033.80