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	$233.26	10.353%	$257.4094	$257.41	$257.40	$257.40
Purchase #2	$186.89	11.682%	$208.7225	$208.72	$208.70	$208.70
Purchase #3	$33.58	11.710%	$37.5122	$37.51	$37.50	$37.50
Purchase #4	$148.91	10.833%	$165.0414	$165.04	$165.05	$165.00
Purchase #5	$78.74	9.712%	$86.3872	$86.39	$86.40	$86.40
Purchase #6	$13.55	7.861%	$14.6152	$14.62	$14.60	$14.60
Purchase #7	$105.99	10.289%	$116.8953	$116.90	$116.90	$116.90
7 purchase totals =	$800.92		$886.5832	$886.59	$886.55	$886.50