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	$164.29	13.399%	$186.3032	$186.30	$186.30	$186.30
Purchase #2	$86.78	3.308%	$89.6507	$89.65	$89.65	$89.70
Purchase #3	$123.86	3.119%	$127.7232	$127.72	$127.70	$127.70
Purchase #4	$145.84	5.219%	$153.4514	$153.45	$153.45	$153.50
Purchase #5	$208.29	6.245%	$221.2977	$221.30	$221.30	$221.30
Purchase #6	$190.90	10.432%	$210.8147	$210.81	$210.80	$210.80
Purchase #7	$45.80	9.589%	$50.1918	$50.19	$50.20	$50.20
7 purchase totals =	$965.76		$1,039.4327	$1,039.42	$1,039.40	$1,039.50