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	$21.41	4.134%	$22.2951	$22.30	$22.30	$22.30
Purchase #2	$230.54	4.500%	$240.9143	$240.91	$240.90	$240.90
Purchase #3	$96.81	5.382%	$102.0203	$102.02	$102.00	$102.00
Purchase #4	$111.54	11.729%	$124.6225	$124.62	$124.60	$124.60
Purchase #5	$117.88	8.144%	$127.4801	$127.48	$127.50	$127.50
Purchase #6	$116.38	12.747%	$131.215	$131.22	$131.20	$131.20
Purchase #7	$209.87	5.494%	$221.4003	$221.40	$221.40	$221.40
7 purchase totals =	$904.43		$969.9476	$969.95	$969.90	$969.90