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	$118.58	7.184%	$127.0988	$127.10	$127.10	$127.10
Purchase #2	$237.83	13.109%	$269.0071	$269.01	$269.00	$269.00
Purchase #3	$189.63	9.384%	$207.4249	$207.42	$207.40	$207.40
Purchase #4	$153.84	11.535%	$171.5854	$171.59	$171.60	$171.60
Purchase #5	$156.58	9.434%	$171.3518	$171.35	$171.35	$171.40
Purchase #6	$78.55	6.820%	$83.9071	$83.91	$83.90	$83.90
Purchase #7	$232.68	11.644%	$259.7733	$259.77	$259.75	$259.80
7 purchase totals =	$1,167.69		$1,290.1484	$1,290.15	$1,290.10	$1,290.20