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	$25.37	12.399%	$28.5156	$28.52	$28.50	$28.50
Purchase #2	$23.79	13.546%	$27.0126	$27.01	$27.00	$27.00
Purchase #3	$195.76	10.105%	$215.5415	$215.54	$215.55	$215.50
Purchase #4	$171.73	6.781%	$183.375	$183.38	$183.40	$183.40
Purchase #5	$211.64	5.490%	$223.259	$223.26	$223.25	$223.30
Purchase #6	$102.71	6.633%	$109.5228	$109.52	$109.50	$109.50
Purchase #7	$103.43	12.718%	$116.5842	$116.58	$116.60	$116.60
7 purchase totals =	$834.43		$903.8107	$903.81	$903.80	$903.80