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	$129.83	13.825%	$147.779	$147.78	$147.80	$147.80
Purchase #2	$122.46	4.248%	$127.6621	$127.66	$127.65	$127.70
Purchase #3	$238.38	10.480%	$263.3622	$263.36	$263.35	$263.40
Purchase #4	$30.67	8.783%	$33.3637	$33.36	$33.35	$33.40
Purchase #5	$236.36	9.783%	$259.4831	$259.48	$259.50	$259.50
Purchase #6	$111.46	3.584%	$115.4547	$115.45	$115.45	$115.50
Purchase #7	$109.26	12.654%	$123.0858	$123.09	$123.10	$123.10
7 purchase totals =	$978.42		$1,070.1906	$1,070.18	$1,070.20	$1,070.40