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	$21.91	10.846%	$24.2864	$24.29	$24.30	$24.30
Purchase #2	$133.29	11.352%	$148.4211	$148.42	$148.40	$148.40
Purchase #3	$176.47	5.382%	$185.9676	$185.97	$185.95	$186.00
Purchase #4	$144.93	12.404%	$162.9071	$162.91	$162.90	$162.90
Purchase #5	$145.31	10.327%	$160.3162	$160.32	$160.30	$160.30
Purchase #6	$169.56	11.602%	$189.2324	$189.23	$189.25	$189.20
Purchase #7	$36.45	5.734%	$38.54	$38.54	$38.55	$38.50
7 purchase totals =	$827.92		$909.6708	$909.68	$909.65	$909.60