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	$100.29	4.156%	$104.4581	$104.46	$104.45	$104.50
Purchase #2	$30.46	6.390%	$32.4064	$32.41	$32.40	$32.40
Purchase #3	$207.92	12.436%	$233.7769	$233.78	$233.80	$233.80
Purchase #4	$208.28	3.437%	$215.4386	$215.44	$215.45	$215.40
Purchase #5	$91.59	13.190%	$103.6707	$103.67	$103.65	$103.70
Purchase #6	$79.65	9.543%	$87.251	$87.25	$87.25	$87.30
Purchase #7	$41.81	7.735%	$45.044	$45.04	$45.05	$45.00
7 purchase totals =	$760.00		$822.0457	$822.05	$822.05	$822.10