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	$159.72	5.474%	$168.4631	$168.46	$168.45	$168.50
Purchase #2	$221.89	13.723%	$252.34	$252.34	$252.35	$252.30
Purchase #3	$213.51	8.139%	$230.8876	$230.89	$230.90	$230.90
Purchase #4	$117.28	5.118%	$123.2824	$123.28	$123.30	$123.30
Purchase #5	$115.70	7.654%	$124.5557	$124.56	$124.55	$124.60
Purchase #6	$78.87	13.789%	$89.7454	$89.75	$89.75	$89.70
Purchase #7	$249.98	4.722%	$261.7841	$261.78	$261.80	$261.80
7 purchase totals =	$1,156.95		$1,251.0583	$1,251.06	$1,251.10	$1,251.10