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	$92.87	11.770%	$103.8008	$103.80	$103.80	$103.80
Purchase #2	$177.77	6.171%	$188.7402	$188.74	$188.75	$188.70
Purchase #3	$62.97	4.325%	$65.6935	$65.69	$65.70	$65.70
Purchase #4	$241.67	9.570%	$264.7978	$264.80	$264.80	$264.80
Purchase #5	$64.85	12.197%	$72.7598	$72.76	$72.75	$72.80
Purchase #6	$89.27	13.715%	$101.5134	$101.51	$101.50	$101.50
Purchase #7	$42.82	9.248%	$46.78	$46.78	$46.80	$46.80
7 purchase totals =	$772.22		$844.0855	$844.08	$844.10	$844.10