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	$78.71	13.242%	$89.1328	$89.13	$89.15	$89.10
Purchase #2	$157.25	3.388%	$162.5776	$162.58	$162.60	$162.60
Purchase #3	$156.69	10.641%	$173.3634	$173.36	$173.35	$173.40
Purchase #4	$39.39	12.418%	$44.2815	$44.28	$44.30	$44.30
Purchase #5	$115.98	10.419%	$128.064	$128.06	$128.05	$128.10
Purchase #6	$166.82	11.379%	$185.8024	$185.80	$185.80	$185.80
Purchase #7	$133.54	11.713%	$149.1815	$149.18	$149.20	$149.20
7 purchase totals =	$848.38		$932.4032	$932.39	$932.45	$932.50