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	$39.41	8.522%	$42.7685	$42.77	$42.75	$42.80
Purchase #2	$65.78	4.806%	$68.9414	$68.94	$68.95	$68.90
Purchase #3	$230.39	10.585%	$254.7768	$254.78	$254.80	$254.80
Purchase #4	$139.46	11.281%	$155.1925	$155.19	$155.20	$155.20
Purchase #5	$89.57	3.765%	$92.9423	$92.94	$92.95	$92.90
Purchase #6	$156.57	10.738%	$173.3825	$173.38	$173.40	$173.40
Purchase #7	$195.60	10.104%	$215.3634	$215.36	$215.35	$215.40
7 purchase totals =	$916.78		$1,003.3674	$1,003.36	$1,003.40	$1,003.40