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	$88.78	12.477%	$99.8571	$99.86	$99.85	$99.90
Purchase #2	$18.37	13.591%	$20.8667	$20.87	$20.85	$20.90
Purchase #3	$89.68	8.731%	$97.51	$97.51	$97.50	$97.50
Purchase #4	$90.67	12.616%	$102.1089	$102.11	$102.10	$102.10
Purchase #5	$156.61	6.123%	$166.1992	$166.20	$166.20	$166.20
Purchase #6	$49.83	7.491%	$53.5628	$53.56	$53.55	$53.60
Purchase #7	$50.46	8.231%	$54.6134	$54.61	$54.60	$54.60
7 purchase totals =	$544.40		$594.7181	$594.72	$594.65	$594.80