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	$81.52	10.471%	$90.056	$90.06	$90.05	$90.10
Purchase #2	$239.66	6.803%	$255.9641	$255.96	$255.95	$256.00
Purchase #3	$92.64	9.316%	$101.2703	$101.27	$101.25	$101.30
Purchase #4	$25.85	4.862%	$27.1068	$27.11	$27.10	$27.10
Purchase #5	$55.67	4.443%	$58.1434	$58.14	$58.15	$58.10
Purchase #6	$96.47	5.698%	$101.9669	$101.97	$101.95	$102.00
Purchase #7	$99.67	3.782%	$103.4395	$103.44	$103.45	$103.40
7 purchase totals =	$691.48		$737.9470	$737.95	$737.90	$738.00