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	$154.99	8.529%	$168.2091	$168.21	$168.20	$168.20
Purchase #2	$204.51	6.755%	$218.3247	$218.32	$218.30	$218.30
Purchase #3	$140.29	7.678%	$151.0615	$151.06	$151.05	$151.10
Purchase #4	$38.70	12.233%	$43.4342	$43.43	$43.45	$43.40
Purchase #5	$64.26	11.844%	$71.871	$71.87	$71.85	$71.90
Purchase #6	$228.32	9.631%	$250.3095	$250.31	$250.30	$250.30
Purchase #7	$81.32	11.739%	$90.8662	$90.87	$90.85	$90.90
7 purchase totals =	$912.39		$994.0762	$994.07	$994.00	$994.10