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	$226.61	12.590%	$255.1402	$255.14	$255.15	$255.10
Purchase #2	$230.72	6.315%	$245.29	$245.29	$245.30	$245.30
Purchase #3	$51.51	8.747%	$56.0156	$56.02	$56.00	$56.00
Purchase #4	$105.84	8.457%	$114.7909	$114.79	$114.80	$114.80
Purchase #5	$161.96	6.448%	$172.4032	$172.40	$172.40	$172.40
Purchase #6	$14.94	6.139%	$15.8572	$15.86	$15.85	$15.90
Purchase #7	$181.70	5.688%	$192.0351	$192.04	$192.05	$192.00
7 purchase totals =	$973.28		$1,051.5322	$1,051.54	$1,051.55	$1,051.50