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	$170.98	12.387%	$192.1593	$192.16	$192.15	$192.20
Purchase #2	$250.26	11.861%	$279.9433	$279.94	$279.95	$279.90
Purchase #3	$97.86	10.489%	$108.1245	$108.12	$108.10	$108.10
Purchase #4	$82.55	3.775%	$85.6663	$85.67	$85.65	$85.70
Purchase #5	$174.97	12.333%	$196.5491	$196.55	$196.55	$196.50
Purchase #6	$84.56	6.504%	$90.0598	$90.06	$90.05	$90.10
Purchase #7	$249.25	3.712%	$258.5022	$258.50	$258.50	$258.50
7 purchase totals =	$1,110.43		$1,211.0045	$1,211.00	$1,210.95	$1,211.00