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	$141.99	9.694%	$155.7545	$155.75	$155.75	$155.80
Purchase #2	$130.33	10.788%	$144.39	$144.39	$144.40	$144.40
Purchase #3	$17.56	5.580%	$18.5398	$18.54	$18.55	$18.50
Purchase #4	$50.45	12.871%	$56.9434	$56.94	$56.95	$56.90
Purchase #5	$145.68	5.385%	$153.5249	$153.52	$153.50	$153.50
Purchase #6	$179.79	4.144%	$187.2405	$187.24	$187.25	$187.20
Purchase #7	$41.26	6.386%	$43.8949	$43.89	$43.90	$43.90
7 purchase totals =	$707.06		$760.2880	$760.27	$760.30	$760.20