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	$53.41	8.387%	$57.8895	$57.89	$57.90	$57.90
Purchase #2	$89.54	4.385%	$93.4663	$93.47	$93.45	$93.50
Purchase #3	$55.88	9.695%	$61.2976	$61.30	$61.30	$61.30
Purchase #4	$226.47	6.798%	$241.8654	$241.87	$241.85	$241.90
Purchase #5	$133.39	8.150%	$144.2613	$144.26	$144.25	$144.30
Purchase #6	$13.25	5.860%	$14.0265	$14.03	$14.05	$14.00
Purchase #7	$174.58	6.505%	$185.9364	$185.94	$185.95	$185.90
7 purchase totals =	$746.52		$798.7430	$798.76	$798.75	$798.80