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	$81.32	11.723%	$90.8531	$90.85	$90.85	$90.90
Purchase #2	$36.67	6.421%	$39.0246	$39.02	$39.00	$39.00
Purchase #3	$173.49	8.497%	$188.2314	$188.23	$188.25	$188.20
Purchase #4	$175.71	5.585%	$185.5234	$185.52	$185.50	$185.50
Purchase #5	$99.68	6.124%	$105.7844	$105.78	$105.80	$105.80
Purchase #6	$68.51	12.548%	$77.1066	$77.11	$77.10	$77.10
Purchase #7	$71.37	9.847%	$78.3978	$78.40	$78.40	$78.40
7 purchase totals =	$706.75		$764.9213	$764.91	$764.90	$764.90