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	$153.33	3.834%	$159.2087	$159.21	$159.20	$159.20
Purchase #2	$192.58	3.140%	$198.627	$198.63	$198.65	$198.60
Purchase #3	$112.30	9.865%	$123.3784	$123.38	$123.40	$123.40
Purchase #4	$44.50	6.435%	$47.3636	$47.36	$47.35	$47.40
Purchase #5	$18.45	11.625%	$20.5948	$20.59	$20.60	$20.60
Purchase #6	$250.54	11.579%	$279.55	$279.55	$279.55	$279.60
Purchase #7	$229.85	4.423%	$240.0163	$240.02	$240.00	$240.00
7 purchase totals =	$1,001.55		$1,068.7388	$1,068.74	$1,068.75	$1,068.80