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	$191.65	12.657%	$215.9071	$215.91	$215.90	$215.90
Purchase #2	$194.28	11.416%	$216.459	$216.46	$216.45	$216.50
Purchase #3	$118.48	7.761%	$127.6752	$127.68	$127.70	$127.70
Purchase #4	$166.81	7.517%	$179.3491	$179.35	$179.35	$179.30
Purchase #5	$151.48	9.724%	$166.2099	$166.21	$166.20	$166.20
Purchase #6	$90.28	4.613%	$94.4446	$94.44	$94.45	$94.40
Purchase #7	$78.32	3.162%	$80.7965	$80.80	$80.80	$80.80
7 purchase totals =	$991.30		$1,080.8414	$1,080.85	$1,080.85	$1,080.80