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	$238.96	4.364%	$249.3882	$249.39	$249.40	$249.40
Purchase #2	$46.55	5.218%	$48.979	$48.98	$49.00	$49.00
Purchase #3	$216.80	13.136%	$245.2788	$245.28	$245.30	$245.30
Purchase #4	$53.76	11.541%	$59.9644	$59.96	$59.95	$60.00
Purchase #5	$247.72	13.819%	$281.9524	$281.95	$281.95	$282.00
Purchase #6	$59.65	3.250%	$61.5886	$61.59	$61.60	$61.60
Purchase #7	$48.82	5.662%	$51.5842	$51.58	$51.60	$51.60
7 purchase totals =	$912.26		$998.7356	$998.73	$998.80	$998.90