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	$155.50	11.801%	$173.8506	$173.85	$173.85	$173.90
Purchase #2	$127.76	11.837%	$142.883	$142.88	$142.90	$142.90
Purchase #3	$81.87	11.126%	$90.9789	$90.98	$91.00	$91.00
Purchase #4	$184.48	5.557%	$194.7316	$194.73	$194.75	$194.70
Purchase #5	$144.82	12.185%	$162.4663	$162.47	$162.45	$162.50
Purchase #6	$6.28	5.757%	$6.6415	$6.64	$6.65	$6.60
Purchase #7	$127.54	12.570%	$143.5718	$143.57	$143.55	$143.60
7 purchase totals =	$828.25		$915.1237	$915.12	$915.15	$915.20