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	$96.25	9.112%	$105.0203	$105.02	$105.00	$105.00
Purchase #2	$155.42	11.569%	$173.4005	$173.40	$173.40	$173.40
Purchase #3	$40.44	4.589%	$42.2958	$42.30	$42.30	$42.30
Purchase #4	$25.32	8.379%	$27.4416	$27.44	$27.45	$27.40
Purchase #5	$158.66	8.203%	$171.6749	$171.67	$171.65	$171.70
Purchase #6	$29.36	9.560%	$32.1668	$32.17	$32.15	$32.20
Purchase #7	$30.36	10.668%	$33.5988	$33.60	$33.60	$33.60
7 purchase totals =	$535.81		$585.5987	$585.60	$585.55	$585.60