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	$9.39	9.720%	$10.3027	$10.30	$10.30	$10.30
Purchase #2	$186.83	5.451%	$197.0141	$197.01	$197.00	$197.00
Purchase #3	$235.33	12.343%	$264.3768	$264.38	$264.40	$264.40
Purchase #4	$113.42	13.530%	$128.7657	$128.77	$128.75	$128.80
Purchase #5	$79.45	13.654%	$90.2981	$90.30	$90.30	$90.30
Purchase #6	$102.82	6.270%	$109.2668	$109.27	$109.25	$109.30
Purchase #7	$151.63	5.140%	$159.4238	$159.42	$159.40	$159.40
7 purchase totals =	$878.87		$959.4480	$959.45	$959.40	$959.50