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	$19.46	5.274%	$20.4863	$20.49	$20.50	$20.50
Purchase #2	$95.45	4.727%	$99.9619	$99.96	$99.95	$100.00
Purchase #3	$134.28	8.809%	$146.1087	$146.11	$146.10	$146.10
Purchase #4	$93.82	12.341%	$105.3983	$105.40	$105.40	$105.40
Purchase #5	$155.59	7.749%	$167.6467	$167.65	$167.65	$167.60
Purchase #6	$36.67	11.468%	$40.8753	$40.88	$40.90	$40.90
Purchase #7	$242.61	5.151%	$255.1068	$255.11	$255.10	$255.10
7 purchase totals =	$777.88		$835.5840	$835.60	$835.60	$835.60