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	$91.80	8.420%	$99.5296	$99.53	$99.55	$99.50
Purchase #2	$81.69	10.496%	$90.2642	$90.26	$90.25	$90.30
Purchase #3	$69.78	12.791%	$78.7056	$78.71	$78.70	$78.70
Purchase #4	$149.59	11.284%	$166.4697	$166.47	$166.45	$166.50
Purchase #5	$5.51	9.507%	$6.0338	$6.03	$6.05	$6.00
Purchase #6	$18.72	3.430%	$19.3621	$19.36	$19.35	$19.40
Purchase #7	$248.41	5.617%	$262.3632	$262.36	$262.35	$262.40
7 purchase totals =	$665.50		$722.7282	$722.72	$722.70	$722.80