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	$25.63	10.348%	$28.2822	$28.28	$28.30	$28.30
Purchase #2	$132.38	12.307%	$148.672	$148.67	$148.65	$148.70
Purchase #3	$133.73	12.708%	$150.7244	$150.72	$150.70	$150.70
Purchase #4	$236.70	8.395%	$256.571	$256.57	$256.55	$256.60
Purchase #5	$15.31	5.799%	$16.1978	$16.20	$16.20	$16.20
Purchase #6	$124.45	5.512%	$131.3097	$131.31	$131.30	$131.30
Purchase #7	$99.52	5.821%	$105.3131	$105.31	$105.30	$105.30
7 purchase totals =	$767.72		$837.0702	$837.06	$837.00	$837.10