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	$38.39	13.315%	$43.5016	$43.50	$43.50	$43.50
Purchase #2	$212.66	4.435%	$222.0915	$222.09	$222.10	$222.10
Purchase #3	$208.66	9.302%	$228.0696	$228.07	$228.05	$228.10
Purchase #4	$58.37	12.287%	$65.5419	$65.54	$65.55	$65.50
Purchase #5	$79.50	13.515%	$90.2444	$90.24	$90.25	$90.20
Purchase #6	$142.44	7.299%	$152.8367	$152.84	$152.85	$152.80
Purchase #7	$29.73	3.520%	$30.7765	$30.78	$30.80	$30.80
7 purchase totals =	$769.75		$833.0622	$833.06	$833.10	$833.00