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	$21.33	13.138%	$24.1323	$24.13	$24.15	$24.10
Purchase #2	$230.31	4.544%	$240.7753	$240.78	$240.80	$240.80
Purchase #3	$200.40	5.243%	$210.907	$210.91	$210.90	$210.90
Purchase #4	$233.94	8.753%	$254.4168	$254.42	$254.40	$254.40
Purchase #5	$24.96	11.715%	$27.8841	$27.88	$27.90	$27.90
Purchase #6	$145.95	7.218%	$156.4847	$156.48	$156.50	$156.50
Purchase #7	$67.42	6.305%	$71.6708	$71.67	$71.65	$71.70
7 purchase totals =	$924.31		$986.2710	$986.27	$986.30	$986.30