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	$96.72	6.664%	$103.1654	$103.17	$103.15	$103.20
Purchase #2	$132.81	9.222%	$145.0577	$145.06	$145.05	$145.10
Purchase #3	$103.64	13.105%	$117.222	$117.22	$117.20	$117.20
Purchase #4	$144.98	6.321%	$154.1442	$154.14	$154.15	$154.10
Purchase #5	$161.30	6.208%	$171.3135	$171.31	$171.30	$171.30
Purchase #6	$92.93	4.234%	$96.8647	$96.86	$96.85	$96.90
Purchase #7	$63.95	12.499%	$71.9431	$71.94	$71.95	$71.90
7 purchase totals =	$796.33		$859.7106	$859.70	$859.65	$859.70