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	$227.73	3.531%	$235.7711	$235.77	$235.75	$235.80
Purchase #2	$28.94	12.257%	$32.4872	$32.49	$32.50	$32.50
Purchase #3	$196.58	9.202%	$214.6693	$214.67	$214.65	$214.70
Purchase #4	$81.62	9.446%	$89.3298	$89.33	$89.35	$89.30
Purchase #5	$89.90	11.857%	$100.5594	$100.56	$100.55	$100.60
Purchase #6	$18.92	8.800%	$20.585	$20.59	$20.60	$20.60
Purchase #7	$237.66	11.547%	$265.1026	$265.10	$265.10	$265.10
7 purchase totals =	$881.35		$958.5044	$958.51	$958.50	$958.60