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	$239.52	4.491%	$250.2768	$250.28	$250.30	$250.30
Purchase #2	$99.25	12.684%	$111.8389	$111.84	$111.85	$111.80
Purchase #3	$39.91	7.429%	$42.8749	$42.87	$42.85	$42.90
Purchase #4	$36.99	9.436%	$40.4804	$40.48	$40.50	$40.50
Purchase #5	$160.98	5.432%	$169.7244	$169.72	$169.70	$169.70
Purchase #6	$103.83	10.341%	$114.5671	$114.57	$114.55	$114.60
Purchase #7	$94.93	11.427%	$105.7777	$105.78	$105.80	$105.80
7 purchase totals =	$775.41		$835.5402	$835.54	$835.55	$835.60