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	$167.96	9.183%	$183.3838	$183.38	$183.40	$183.40
Purchase #2	$36.53	11.194%	$40.6192	$40.62	$40.60	$40.60
Purchase #3	$80.67	11.589%	$90.0188	$90.02	$90.00	$90.00
Purchase #4	$67.51	9.669%	$74.0375	$74.04	$74.05	$74.00
Purchase #5	$144.65	7.513%	$155.5176	$155.52	$155.50	$155.50
Purchase #6	$198.56	8.699%	$215.8327	$215.83	$215.85	$215.80
Purchase #7	$92.35	4.641%	$96.636	$96.64	$96.65	$96.60
7 purchase totals =	$788.23		$856.0456	$856.05	$856.05	$855.90