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	$56.82	12.814%	$64.1009	$64.10	$64.10	$64.10
Purchase #2	$171.57	12.248%	$192.5839	$192.58	$192.60	$192.60
Purchase #3	$127.82	11.621%	$142.674	$142.67	$142.65	$142.70
Purchase #4	$162.58	5.818%	$172.0389	$172.04	$172.05	$172.00
Purchase #5	$66.93	9.684%	$73.4115	$73.41	$73.40	$73.40
Purchase #6	$80.40	4.201%	$83.7776	$83.78	$83.80	$83.80
Purchase #7	$82.48	9.263%	$90.1201	$90.12	$90.10	$90.10
7 purchase totals =	$748.60		$818.7069	$818.70	$818.70	$818.70