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	$78.33	6.680%	$83.5624	$83.56	$83.55	$83.60
Purchase #2	$42.79	3.200%	$44.1593	$44.16	$44.15	$44.20
Purchase #3	$39.96	5.162%	$42.0227	$42.02	$42.00	$42.00
Purchase #4	$153.57	8.300%	$166.3163	$166.32	$166.30	$166.30
Purchase #5	$51.26	5.522%	$54.0906	$54.09	$54.10	$54.10
Purchase #6	$180.37	7.718%	$194.291	$194.29	$194.30	$194.30
Purchase #7	$150.28	6.521%	$160.0798	$160.08	$160.10	$160.10
7 purchase totals =	$696.56		$744.5221	$744.52	$744.50	$744.60