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	$85.56	6.106%	$90.7843	$90.78	$90.80	$90.80
Purchase #2	$82.94	9.853%	$91.1121	$91.11	$91.10	$91.10
Purchase #3	$173.54	12.235%	$194.7726	$194.77	$194.75	$194.80
Purchase #4	$130.64	4.409%	$136.3999	$136.40	$136.40	$136.40
Purchase #5	$225.58	3.749%	$234.037	$234.04	$234.05	$234.00
Purchase #6	$57.78	3.190%	$59.6232	$59.62	$59.60	$59.60
Purchase #7	$108.98	12.817%	$122.948	$122.95	$122.95	$122.90
7 purchase totals =	$865.02		$929.6771	$929.67	$929.65	$929.60