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	$165.74	13.136%	$187.5116	$187.51	$187.50	$187.50
Purchase #2	$192.85	9.501%	$211.1727	$211.17	$211.15	$211.20
Purchase #3	$234.96	10.443%	$259.4969	$259.50	$259.50	$259.50
Purchase #4	$153.64	11.866%	$171.8709	$171.87	$171.85	$171.90
Purchase #5	$134.52	6.598%	$143.3956	$143.40	$143.40	$143.40
Purchase #6	$35.69	10.150%	$39.3125	$39.31	$39.30	$39.30
Purchase #7	$131.35	7.533%	$141.2446	$141.24	$141.25	$141.20
7 purchase totals =	$1,048.75		$1,154.0048	$1,154.00	$1,153.95	$1,154.00