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	$170.73	10.435%	$188.5457	$188.55	$188.55	$188.50
Purchase #2	$145.64	4.663%	$152.4312	$152.43	$152.45	$152.40
Purchase #3	$44.70	10.332%	$49.3184	$49.32	$49.30	$49.30
Purchase #4	$79.25	12.587%	$89.2252	$89.23	$89.25	$89.20
Purchase #5	$166.87	13.781%	$189.8664	$189.87	$189.85	$189.90
Purchase #6	$142.73	10.749%	$158.072	$158.07	$158.05	$158.10
Purchase #7	$70.61	6.292%	$75.0528	$75.05	$75.05	$75.10
7 purchase totals =	$820.53		$902.5117	$902.52	$902.50	$902.50