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	$156.74	13.814%	$178.3921	$178.39	$178.40	$178.40
Purchase #2	$129.61	13.440%	$147.0296	$147.03	$147.05	$147.00
Purchase #3	$83.52	3.542%	$86.4783	$86.48	$86.50	$86.50
Purchase #4	$111.39	5.707%	$117.747	$117.75	$117.75	$117.70
Purchase #5	$126.69	8.441%	$137.3839	$137.38	$137.40	$137.40
Purchase #6	$141.52	5.123%	$148.7701	$148.77	$148.75	$148.80
Purchase #7	$250.83	5.832%	$265.4584	$265.46	$265.45	$265.50
7 purchase totals =	$1,000.30		$1,081.2594	$1,081.26	$1,081.30	$1,081.30