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	$27.86	5.579%	$29.4143	$29.41	$29.40	$29.40
Purchase #2	$91.70	9.472%	$100.3858	$100.39	$100.40	$100.40
Purchase #3	$32.59	4.801%	$34.1546	$34.15	$34.15	$34.20
Purchase #4	$224.91	10.168%	$247.7788	$247.78	$247.80	$247.80
Purchase #5	$186.98	4.567%	$195.5194	$195.52	$195.50	$195.50
Purchase #6	$174.76	6.207%	$185.6074	$185.61	$185.60	$185.60
Purchase #7	$247.88	5.861%	$262.4082	$262.41	$262.40	$262.40
7 purchase totals =	$986.68		$1,055.2685	$1,055.27	$1,055.25	$1,055.30