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	$248.32	9.678%	$272.3524	$272.35	$272.35	$272.40
Purchase #2	$38.30	5.453%	$40.3885	$40.39	$40.40	$40.40
Purchase #3	$134.69	7.657%	$145.0032	$145.00	$145.00	$145.00
Purchase #4	$76.53	7.837%	$82.5277	$82.53	$82.55	$82.50
Purchase #5	$92.73	13.236%	$105.0037	$105.00	$105.00	$105.00
Purchase #6	$12.30	5.749%	$13.0071	$13.01	$13.00	$13.00
Purchase #7	$122.33	4.185%	$127.4495	$127.45	$127.45	$127.40
7 purchase totals =	$725.20		$785.7321	$785.73	$785.75	$785.70