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	$114.83	10.865%	$127.3063	$127.31	$127.30	$127.30
Purchase #2	$197.54	6.379%	$210.1411	$210.14	$210.15	$210.10
Purchase #3	$138.31	9.141%	$150.9529	$150.95	$150.95	$151.00
Purchase #4	$162.73	5.142%	$171.0976	$171.10	$171.10	$171.10
Purchase #5	$32.36	4.693%	$33.8787	$33.88	$33.90	$33.90
Purchase #6	$192.76	12.383%	$216.6295	$216.63	$216.65	$216.60
Purchase #7	$168.70	6.328%	$179.3753	$179.38	$179.40	$179.40
7 purchase totals =	$1,007.23		$1,089.3814	$1,089.39	$1,089.45	$1,089.40