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	$96.67	4.768%	$101.2792	$101.28	$101.30	$101.30
Purchase #2	$164.57	10.734%	$182.2349	$182.23	$182.25	$182.20
Purchase #3	$123.40	3.298%	$127.4697	$127.47	$127.45	$127.50
Purchase #4	$113.76	9.109%	$124.1224	$124.12	$124.10	$124.10
Purchase #5	$67.64	6.551%	$72.0711	$72.07	$72.05	$72.10
Purchase #6	$160.74	5.826%	$170.1047	$170.10	$170.10	$170.10
Purchase #7	$137.72	3.453%	$142.4755	$142.48	$142.50	$142.50
7 purchase totals =	$864.50		$919.7575	$919.75	$919.75	$919.80