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	$135.79	12.505%	$152.7705	$152.77	$152.75	$152.80
Purchase #2	$172.85	3.804%	$179.4252	$179.43	$179.45	$179.40
Purchase #3	$170.81	12.239%	$191.7154	$191.72	$191.70	$191.70
Purchase #4	$169.54	11.842%	$189.6169	$189.62	$189.60	$189.60
Purchase #5	$140.83	12.321%	$158.1817	$158.18	$158.20	$158.20
Purchase #6	$142.50	4.280%	$148.599	$148.60	$148.60	$148.60
Purchase #7	$127.35	8.782%	$138.5339	$138.53	$138.55	$138.50
7 purchase totals =	$1,059.67		$1,158.8426	$1,158.85	$1,158.85	$1,158.80