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	$250.90	11.718%	$280.3005	$280.30	$280.30	$280.30
Purchase #2	$11.90	13.289%	$13.4814	$13.48	$13.50	$13.50
Purchase #3	$151.31	10.712%	$167.5183	$167.52	$167.50	$167.50
Purchase #4	$162.86	7.642%	$175.3058	$175.31	$175.30	$175.30
Purchase #5	$145.77	4.149%	$151.818	$151.82	$151.80	$151.80
Purchase #6	$134.63	4.864%	$141.1784	$141.18	$141.20	$141.20
Purchase #7	$161.95	13.131%	$183.2157	$183.22	$183.20	$183.20
7 purchase totals =	$1,019.32		$1,112.8181	$1,112.83	$1,112.80	$1,112.80