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	$231.94	7.522%	$249.3865	$249.39	$249.40	$249.40
Purchase #2	$142.92	12.498%	$160.7821	$160.78	$160.80	$160.80
Purchase #3	$184.51	8.446%	$200.0937	$200.09	$200.10	$200.10
Purchase #4	$138.85	5.546%	$146.5506	$146.55	$146.55	$146.60
Purchase #5	$148.26	13.529%	$168.3181	$168.32	$168.30	$168.30
Purchase #6	$19.93	3.343%	$20.5963	$20.60	$20.60	$20.60
Purchase #7	$71.87	9.521%	$78.7127	$78.71	$78.70	$78.70
7 purchase totals =	$938.28		$1,024.4400	$1,024.44	$1,024.45	$1,024.50