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	$250.76	4.273%	$261.475	$261.48	$261.50	$261.50
Purchase #2	$95.99	7.471%	$103.1614	$103.16	$103.15	$103.20
Purchase #3	$55.91	9.842%	$61.4127	$61.41	$61.40	$61.40
Purchase #4	$96.75	3.265%	$99.9089	$99.91	$99.90	$99.90
Purchase #5	$148.86	11.636%	$166.1813	$166.18	$166.20	$166.20
Purchase #6	$158.41	8.658%	$172.1251	$172.13	$172.15	$172.10
Purchase #7	$75.79	8.519%	$82.2466	$82.25	$82.25	$82.20
7 purchase totals =	$882.47		$946.5110	$946.52	$946.55	$946.50