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	$208.97	9.844%	$229.541	$229.54	$229.55	$229.50
Purchase #2	$91.59	13.121%	$103.6075	$103.61	$103.60	$103.60
Purchase #3	$26.38	5.269%	$27.77	$27.77	$27.75	$27.80
Purchase #4	$155.98	6.504%	$166.1249	$166.12	$166.10	$166.10
Purchase #5	$55.58	4.419%	$58.0361	$58.04	$58.05	$58.00
Purchase #6	$32.56	3.497%	$33.6986	$33.70	$33.70	$33.70
Purchase #7	$20.31	6.349%	$21.5995	$21.60	$21.60	$21.60
7 purchase totals =	$591.37		$640.3776	$640.38	$640.35	$640.30