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	$111.39	11.192%	$123.8568	$123.86	$123.85	$123.90
Purchase #2	$95.49	8.345%	$103.4586	$103.46	$103.45	$103.50
Purchase #3	$118.39	8.305%	$128.2223	$128.22	$128.20	$128.20
Purchase #4	$123.88	7.370%	$133.01	$133.01	$133.00	$133.00
Purchase #5	$60.47	11.546%	$67.4519	$67.45	$67.45	$67.50
Purchase #6	$18.91	13.154%	$21.3974	$21.40	$21.40	$21.40
Purchase #7	$233.27	12.843%	$263.2289	$263.23	$263.25	$263.20
7 purchase totals =	$761.80		$840.6259	$840.63	$840.60	$840.70