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	$109.71	5.306%	$115.5312	$115.53	$115.55	$115.50
Purchase #2	$249.89	9.570%	$273.8045	$273.80	$273.80	$273.80
Purchase #3	$28.94	10.397%	$31.9489	$31.95	$31.95	$31.90
Purchase #4	$118.94	10.547%	$131.4846	$131.48	$131.50	$131.50
Purchase #5	$59.64	4.409%	$62.2695	$62.27	$62.25	$62.30
Purchase #6	$45.46	11.683%	$50.7711	$50.77	$50.75	$50.80
Purchase #7	$215.45	13.852%	$245.2941	$245.29	$245.30	$245.30
7 purchase totals =	$828.03		$911.1039	$911.09	$911.10	$911.10