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	$25.77	10.786%	$28.5496	$28.55	$28.55	$28.50
Purchase #2	$27.69	5.645%	$29.2531	$29.25	$29.25	$29.30
Purchase #3	$46.29	6.138%	$49.1313	$49.13	$49.15	$49.10
Purchase #4	$168.28	3.115%	$173.5219	$173.52	$173.50	$173.50
Purchase #5	$134.49	6.729%	$143.5398	$143.54	$143.55	$143.50
Purchase #6	$67.37	5.525%	$71.0922	$71.09	$71.10	$71.10
Purchase #7	$242.63	5.673%	$256.3944	$256.39	$256.40	$256.40
7 purchase totals =	$712.52		$751.4823	$751.47	$751.50	$751.40