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	$150.71	13.675%	$171.3196	$171.32	$171.30	$171.30
Purchase #2	$179.87	10.168%	$198.1592	$198.16	$198.15	$198.20
Purchase #3	$122.55	5.665%	$129.4925	$129.49	$129.50	$129.50
Purchase #4	$129.78	11.848%	$145.1563	$145.16	$145.15	$145.20
Purchase #5	$124.80	13.466%	$141.6056	$141.61	$141.60	$141.60
Purchase #6	$243.74	6.500%	$259.5831	$259.58	$259.60	$259.60
Purchase #7	$131.87	7.204%	$141.3699	$141.37	$141.35	$141.40
7 purchase totals =	$1,083.32		$1,186.6862	$1,186.69	$1,186.65	$1,186.80