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	$180.78	4.286%	$188.5282	$188.53	$188.55	$188.50
Purchase #2	$50.65	3.163%	$52.2521	$52.25	$52.25	$52.30
Purchase #3	$177.77	7.874%	$191.7676	$191.77	$191.75	$191.80
Purchase #4	$154.95	10.696%	$171.5235	$171.52	$171.50	$171.50
Purchase #5	$134.65	4.315%	$140.4601	$140.46	$140.45	$140.50
Purchase #6	$114.93	3.288%	$118.7089	$118.71	$118.70	$118.70
Purchase #7	$73.86	12.397%	$83.0164	$83.02	$83.00	$83.00
7 purchase totals =	$887.59		$946.2568	$946.26	$946.20	$946.30