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	$79.28	13.557%	$90.028	$90.03	$90.05	$90.00
Purchase #2	$163.91	11.573%	$182.8793	$182.88	$182.90	$182.90
Purchase #3	$208.98	6.182%	$221.8991	$221.90	$221.90	$221.90
Purchase #4	$164.79	5.208%	$173.3723	$173.37	$173.35	$173.40
Purchase #5	$243.26	8.829%	$264.7374	$264.74	$264.75	$264.70
Purchase #6	$78.39	4.789%	$82.1441	$82.14	$82.15	$82.10
Purchase #7	$199.68	3.726%	$207.1201	$207.12	$207.10	$207.10
7 purchase totals =	$1,138.29		$1,222.1803	$1,222.18	$1,222.20	$1,222.10