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	$79.44	12.701%	$89.5297	$89.53	$89.55	$89.50
Purchase #2	$207.41	8.599%	$225.2452	$225.25	$225.25	$225.20
Purchase #3	$131.89	13.794%	$150.0829	$150.08	$150.10	$150.10
Purchase #4	$225.94	7.308%	$242.4517	$242.45	$242.45	$242.50
Purchase #5	$43.75	3.356%	$45.2183	$45.22	$45.20	$45.20
Purchase #6	$200.79	10.364%	$221.5999	$221.60	$221.60	$221.60
Purchase #7	$138.50	3.286%	$143.0511	$143.05	$143.05	$143.10
7 purchase totals =	$1,027.72		$1,117.1788	$1,117.18	$1,117.20	$1,117.20