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	$38.71	8.714%	$42.0832	$42.08	$42.10	$42.10
Purchase #2	$189.57	13.451%	$215.0691	$215.07	$215.05	$215.10
Purchase #3	$201.29	9.748%	$220.9117	$220.91	$220.90	$220.90
Purchase #4	$144.67	11.216%	$160.8962	$160.90	$160.90	$160.90
Purchase #5	$115.47	10.164%	$127.2064	$127.21	$127.20	$127.20
Purchase #6	$86.25	3.464%	$89.2377	$89.24	$89.25	$89.20
Purchase #7	$173.82	11.569%	$193.9292	$193.93	$193.95	$193.90
7 purchase totals =	$949.78		$1,049.3335	$1,049.34	$1,049.35	$1,049.30