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	$71.79	3.710%	$74.4534	$74.45	$74.45	$74.50
Purchase #2	$243.78	8.648%	$264.8621	$264.86	$264.85	$264.90
Purchase #3	$75.75	6.789%	$80.8927	$80.89	$80.90	$80.90
Purchase #4	$74.69	7.152%	$80.0318	$80.03	$80.05	$80.00
Purchase #5	$180.37	5.546%	$190.3733	$190.37	$190.35	$190.40
Purchase #6	$178.64	4.833%	$187.2737	$187.27	$187.25	$187.30
Purchase #7	$117.31	9.329%	$128.2538	$128.25	$128.25	$128.30
7 purchase totals =	$942.33		$1,006.1408	$1,006.12	$1,006.10	$1,006.30