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	$125.40	12.120%	$140.5985	$140.60	$140.60	$140.60
Purchase #2	$250.50	11.206%	$278.571	$278.57	$278.55	$278.60
Purchase #3	$37.69	13.110%	$42.6312	$42.63	$42.65	$42.60
Purchase #4	$149.51	3.727%	$155.0822	$155.08	$155.10	$155.10
Purchase #5	$172.77	13.781%	$196.5794	$196.58	$196.60	$196.60
Purchase #6	$73.49	7.554%	$79.0414	$79.04	$79.05	$79.00
Purchase #7	$57.74	4.558%	$60.3718	$60.37	$60.35	$60.40
7 purchase totals =	$867.10		$952.8755	$952.87	$952.90	$952.90