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	$143.34	8.840%	$156.0113	$156.01	$156.00	$156.00
Purchase #2	$96.75	6.747%	$103.2777	$103.28	$103.30	$103.30
Purchase #3	$245.60	13.357%	$278.4048	$278.40	$278.40	$278.40
Purchase #4	$51.76	8.781%	$56.305	$56.31	$56.30	$56.30
Purchase #5	$106.92	11.611%	$119.3345	$119.33	$119.35	$119.30
Purchase #6	$173.52	9.509%	$190.02	$190.02	$190.00	$190.00
Purchase #7	$39.84	13.224%	$45.1084	$45.11	$45.10	$45.10
7 purchase totals =	$857.73		$948.4617	$948.46	$948.45	$948.40