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	$112.38	13.626%	$127.6929	$127.69	$127.70	$127.70
Purchase #2	$83.52	7.791%	$90.027	$90.03	$90.05	$90.00
Purchase #3	$33.73	11.393%	$37.5729	$37.57	$37.55	$37.60
Purchase #4	$160.70	8.342%	$174.1056	$174.11	$174.10	$174.10
Purchase #5	$246.89	3.174%	$254.7263	$254.73	$254.75	$254.70
Purchase #6	$169.71	13.190%	$192.0947	$192.09	$192.10	$192.10
Purchase #7	$66.50	9.743%	$72.9791	$72.98	$73.00	$73.00
7 purchase totals =	$873.43		$949.1985	$949.20	$949.25	$949.20