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	$242.37	8.865%	$263.8561	$263.86	$263.85	$263.90
Purchase #2	$82.50	9.588%	$90.4101	$90.41	$90.40	$90.40
Purchase #3	$19.62	10.368%	$21.6542	$21.65	$21.65	$21.70
Purchase #4	$57.48	3.162%	$59.2975	$59.30	$59.30	$59.30
Purchase #5	$103.37	13.359%	$117.1792	$117.18	$117.20	$117.20
Purchase #6	$13.67	6.550%	$14.5654	$14.57	$14.55	$14.60
Purchase #7	$84.96	11.146%	$94.4296	$94.43	$94.45	$94.40
7 purchase totals =	$603.97		$661.3921	$661.40	$661.40	$661.50