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	$124.96	7.732%	$134.6219	$134.62	$134.60	$134.60
Purchase #2	$239.94	10.475%	$265.0737	$265.07	$265.05	$265.10
Purchase #3	$97.66	7.754%	$105.2326	$105.23	$105.25	$105.20
Purchase #4	$113.55	8.469%	$123.1665	$123.17	$123.15	$123.20
Purchase #5	$25.83	5.776%	$27.3219	$27.32	$27.30	$27.30
Purchase #6	$84.69	13.862%	$96.4297	$96.43	$96.45	$96.40
Purchase #7	$123.44	3.517%	$127.7814	$127.78	$127.80	$127.80
7 purchase totals =	$810.07		$879.6277	$879.62	$879.60	$879.60