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	$129.46	11.542%	$144.4023	$144.40	$144.40	$144.40
Purchase #2	$168.49	12.210%	$189.0626	$189.06	$189.05	$189.10
Purchase #3	$79.83	7.716%	$85.9897	$85.99	$86.00	$86.00
Purchase #4	$160.62	6.829%	$171.5887	$171.59	$171.60	$171.60
Purchase #5	$94.92	5.384%	$100.0305	$100.03	$100.05	$100.00
Purchase #6	$48.41	10.590%	$53.5366	$53.54	$53.55	$53.50
Purchase #7	$43.36	4.830%	$45.4543	$45.45	$45.45	$45.50
7 purchase totals =	$725.09		$790.0647	$790.06	$790.10	$790.10