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	$178.71	4.285%	$186.3677	$186.37	$186.35	$186.40
Purchase #2	$156.61	5.630%	$165.4271	$165.43	$165.45	$165.40
Purchase #3	$80.40	10.199%	$88.6	$88.60	$88.60	$88.60
Purchase #4	$108.68	3.239%	$112.2001	$112.20	$112.20	$112.20
Purchase #5	$147.49	13.569%	$167.5029	$167.50	$167.50	$167.50
Purchase #6	$41.56	11.152%	$46.1948	$46.19	$46.20	$46.20
Purchase #7	$60.89	8.535%	$66.087	$66.09	$66.10	$66.10
7 purchase totals =	$774.34		$832.3796	$832.38	$832.40	$832.40