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	$73.72	3.782%	$76.5081	$76.51	$76.50	$76.50
Purchase #2	$218.45	10.284%	$240.9154	$240.92	$240.90	$240.90
Purchase #3	$205.38	6.149%	$218.0088	$218.01	$218.00	$218.00
Purchase #4	$59.77	12.420%	$67.1934	$67.19	$67.20	$67.20
Purchase #5	$49.55	9.697%	$54.3549	$54.35	$54.35	$54.40
Purchase #6	$81.97	9.152%	$89.4719	$89.47	$89.45	$89.50
Purchase #7	$194.61	6.610%	$207.4737	$207.47	$207.45	$207.50
7 purchase totals =	$883.45		$953.9262	$953.92	$953.85	$954.00