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	$120.89	3.301%	$124.8806	$124.88	$124.90	$124.90
Purchase #2	$29.57	11.406%	$32.9428	$32.94	$32.95	$32.90
Purchase #3	$28.89	11.438%	$32.1944	$32.19	$32.20	$32.20
Purchase #4	$79.42	4.355%	$82.8787	$82.88	$82.90	$82.90
Purchase #5	$238.82	11.589%	$266.4968	$266.50	$266.50	$266.50
Purchase #6	$127.49	4.389%	$133.0855	$133.09	$133.10	$133.10
Purchase #7	$246.52	8.699%	$267.9648	$267.96	$267.95	$268.00
7 purchase totals =	$871.60		$940.4436	$940.44	$940.50	$940.50