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	$242.58	4.657%	$253.877	$253.88	$253.90	$253.90
Purchase #2	$108.28	8.194%	$117.1525	$117.15	$117.15	$117.20
Purchase #3	$134.36	5.805%	$142.1596	$142.16	$142.15	$142.20
Purchase #4	$86.41	13.826%	$98.357	$98.36	$98.35	$98.40
Purchase #5	$80.25	13.184%	$90.8302	$90.83	$90.85	$90.80
Purchase #6	$30.58	7.845%	$32.979	$32.98	$33.00	$33.00
Purchase #7	$159.85	12.693%	$180.1398	$180.14	$180.15	$180.10
7 purchase totals =	$842.31		$915.4951	$915.50	$915.55	$915.60