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	$48.48	12.643%	$54.6093	$54.61	$54.60	$54.60
Purchase #2	$76.31	7.870%	$82.3156	$82.32	$82.30	$82.30
Purchase #3	$16.58	13.404%	$18.8024	$18.80	$18.80	$18.80
Purchase #4	$159.73	11.836%	$178.6356	$178.64	$178.65	$178.60
Purchase #5	$127.61	13.134%	$144.3703	$144.37	$144.35	$144.40
Purchase #6	$53.60	13.127%	$60.6361	$60.64	$60.65	$60.60
Purchase #7	$61.59	4.408%	$64.3049	$64.30	$64.30	$64.30
7 purchase totals =	$543.90		$603.6742	$603.68	$603.65	$603.60