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	$81.58	10.321%	$89.9999	$90.00	$90.00	$90.00
Purchase #2	$62.29	9.268%	$68.063	$68.06	$68.05	$68.10
Purchase #3	$20.69	13.365%	$23.4552	$23.46	$23.45	$23.50
Purchase #4	$99.51	12.741%	$112.1886	$112.19	$112.20	$112.20
Purchase #5	$135.60	12.290%	$152.2652	$152.27	$152.25	$152.30
Purchase #6	$180.52	5.214%	$189.9323	$189.93	$189.95	$189.90
Purchase #7	$89.82	4.815%	$94.1448	$94.14	$94.15	$94.10
7 purchase totals =	$670.01		$730.0490	$730.05	$730.05	$730.10