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	$242.38	8.761%	$263.6149	$263.61	$263.60	$263.60
Purchase #2	$140.57	5.717%	$148.6064	$148.61	$148.60	$148.60
Purchase #3	$119.85	6.457%	$127.5887	$127.59	$127.60	$127.60
Purchase #4	$55.86	6.419%	$59.4457	$59.45	$59.45	$59.40
Purchase #5	$32.93	3.120%	$33.9574	$33.96	$33.95	$34.00
Purchase #6	$84.79	9.301%	$92.6763	$92.68	$92.70	$92.70
Purchase #7	$62.81	9.737%	$68.9258	$68.93	$68.95	$68.90
7 purchase totals =	$739.19		$794.8152	$794.83	$794.85	$794.80