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	$75.65	8.509%	$82.0871	$82.09	$82.10	$82.10
Purchase #2	$66.57	11.346%	$74.123	$74.12	$74.10	$74.10
Purchase #3	$176.55	3.637%	$182.9711	$182.97	$182.95	$183.00
Purchase #4	$55.76	10.367%	$61.5406	$61.54	$61.55	$61.50
Purchase #5	$6.66	7.134%	$7.1351	$7.14	$7.15	$7.10
Purchase #6	$41.65	6.722%	$44.4497	$44.45	$44.45	$44.40
Purchase #7	$76.82	8.538%	$83.3789	$83.38	$83.40	$83.40
7 purchase totals =	$499.66		$535.6855	$535.69	$535.70	$535.60