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	$19.67	3.285%	$20.3162	$20.32	$20.30	$20.30
Purchase #2	$119.69	10.298%	$132.0157	$132.02	$132.00	$132.00
Purchase #3	$101.50	9.786%	$111.4328	$111.43	$111.45	$111.40
Purchase #4	$212.33	9.826%	$233.1935	$233.19	$233.20	$233.20
Purchase #5	$114.96	7.122%	$123.1475	$123.15	$123.15	$123.10
Purchase #6	$73.72	10.710%	$81.6154	$81.62	$81.60	$81.60
Purchase #7	$147.42	8.500%	$159.9507	$159.95	$159.95	$160.00
7 purchase totals =	$789.29		$861.6718	$861.68	$861.65	$861.60