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	$74.64	8.491%	$80.9777	$80.98	$81.00	$81.00
Purchase #2	$192.40	4.380%	$200.8271	$200.83	$200.85	$200.80
Purchase #3	$130.57	7.316%	$140.1225	$140.12	$140.10	$140.10
Purchase #4	$159.74	13.734%	$181.6787	$181.68	$181.70	$181.70
Purchase #5	$108.50	10.549%	$119.9457	$119.95	$119.95	$119.90
Purchase #6	$43.55	4.523%	$45.5198	$45.52	$45.50	$45.50
Purchase #7	$162.28	7.109%	$173.8165	$173.82	$173.80	$173.80
7 purchase totals =	$871.68		$942.8880	$942.90	$942.90	$942.80