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	$182.41	5.140%	$191.7859	$191.79	$191.80	$191.80
Purchase #2	$89.88	11.272%	$100.0113	$100.01	$100.00	$100.00
Purchase #3	$91.68	9.728%	$100.5986	$100.60	$100.60	$100.60
Purchase #4	$146.54	12.376%	$164.6758	$164.68	$164.70	$164.70
Purchase #5	$140.72	3.407%	$145.5143	$145.51	$145.50	$145.50
Purchase #6	$100.47	3.309%	$103.7946	$103.79	$103.80	$103.80
Purchase #7	$89.56	5.248%	$94.2601	$94.26	$94.25	$94.30
7 purchase totals =	$841.26		$900.6406	$900.64	$900.65	$900.70