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	$41.96	10.771%	$46.4795	$46.48	$46.50	$46.50
Purchase #2	$176.70	5.602%	$186.5987	$186.60	$186.60	$186.60
Purchase #3	$84.59	5.793%	$89.4903	$89.49	$89.50	$89.50
Purchase #4	$199.97	9.656%	$219.2791	$219.28	$219.30	$219.30
Purchase #5	$238.57	10.632%	$263.9348	$263.93	$263.95	$263.90
Purchase #6	$82.55	9.233%	$90.1718	$90.17	$90.15	$90.20
Purchase #7	$21.29	4.664%	$22.283	$22.28	$22.30	$22.30
7 purchase totals =	$845.63		$918.2372	$918.23	$918.30	$918.30