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	$79.85	11.538%	$89.0631	$89.06	$89.05	$89.10
Purchase #2	$103.75	6.314%	$110.3008	$110.30	$110.30	$110.30
Purchase #3	$159.60	11.514%	$177.9763	$177.98	$178.00	$178.00
Purchase #4	$164.46	4.862%	$172.456	$172.46	$172.45	$172.50
Purchase #5	$66.43	9.582%	$72.7953	$72.80	$72.80	$72.80
Purchase #6	$155.39	10.424%	$171.5879	$171.59	$171.60	$171.60
Purchase #7	$119.91	11.288%	$133.4454	$133.45	$133.45	$133.40
7 purchase totals =	$849.39		$927.6248	$927.64	$927.65	$927.70