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	$135.73	11.836%	$151.795	$151.80	$151.80	$151.80
Purchase #2	$99.44	9.848%	$109.2329	$109.23	$109.25	$109.20
Purchase #3	$150.99	11.459%	$168.2919	$168.29	$168.30	$168.30
Purchase #4	$160.62	12.462%	$180.6365	$180.64	$180.65	$180.60
Purchase #5	$92.91	13.767%	$105.7009	$105.70	$105.70	$105.70
Purchase #6	$71.27	9.350%	$77.9337	$77.93	$77.95	$77.90
Purchase #7	$138.93	5.650%	$146.7795	$146.78	$146.80	$146.80
7 purchase totals =	$849.89		$940.3704	$940.37	$940.45	$940.30