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	$235.72	13.824%	$268.3059	$268.31	$268.30	$268.30
Purchase #2	$166.34	5.606%	$175.665	$175.67	$175.65	$175.70
Purchase #3	$37.27	8.766%	$40.5371	$40.54	$40.55	$40.50
Purchase #4	$92.91	10.772%	$102.9183	$102.92	$102.90	$102.90
Purchase #5	$104.75	3.549%	$108.4676	$108.47	$108.45	$108.50
Purchase #6	$139.32	10.864%	$154.4557	$154.46	$154.45	$154.50
Purchase #7	$173.82	8.215%	$188.0993	$188.10	$188.10	$188.10
7 purchase totals =	$950.13		$1,038.4489	$1,038.47	$1,038.40	$1,038.50