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	$66.88	3.795%	$69.4181	$69.42	$69.40	$69.40
Purchase #2	$130.95	13.579%	$148.7317	$148.73	$148.75	$148.70
Purchase #3	$77.52	11.370%	$86.334	$86.33	$86.35	$86.30
Purchase #4	$81.59	12.294%	$91.6207	$91.62	$91.60	$91.60
Purchase #5	$121.45	12.200%	$136.2669	$136.27	$136.25	$136.30
Purchase #6	$19.78	9.293%	$21.6182	$21.62	$21.60	$21.60
Purchase #7	$84.79	6.637%	$90.4175	$90.42	$90.40	$90.40
7 purchase totals =	$582.96		$644.4071	$644.41	$644.35	$644.30