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	$72.76	5.160%	$76.5144	$76.51	$76.50	$76.50
Purchase #2	$45.79	6.744%	$48.8781	$48.88	$48.90	$48.90
Purchase #3	$42.87	8.333%	$46.4424	$46.44	$46.45	$46.40
Purchase #4	$156.88	10.472%	$173.3085	$173.31	$173.30	$173.30
Purchase #5	$223.93	4.171%	$233.2701	$233.27	$233.25	$233.30
Purchase #6	$112.92	6.256%	$119.9843	$119.98	$120.00	$120.00
Purchase #7	$74.57	9.351%	$81.543	$81.54	$81.55	$81.50
7 purchase totals =	$729.72		$779.9408	$779.93	$779.95	$779.90