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	$206.98	6.256%	$219.9287	$219.93	$219.95	$219.90
Purchase #2	$101.92	4.603%	$106.6114	$106.61	$106.60	$106.60
Purchase #3	$123.51	10.734%	$136.7676	$136.77	$136.75	$136.80
Purchase #4	$74.72	13.729%	$84.9783	$84.98	$85.00	$85.00
Purchase #5	$168.31	10.435%	$185.8731	$185.87	$185.85	$185.90
Purchase #6	$105.64	3.501%	$109.3385	$109.34	$109.35	$109.30
Purchase #7	$236.98	10.439%	$261.7183	$261.72	$261.70	$261.70
7 purchase totals =	$1,018.06		$1,105.2159	$1,105.22	$1,105.20	$1,105.20