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	$181.47	3.818%	$188.3985	$188.40	$188.40	$188.40
Purchase #2	$207.47	9.693%	$227.5801	$227.58	$227.60	$227.60
Purchase #3	$217.64	10.410%	$240.2963	$240.30	$240.30	$240.30
Purchase #4	$151.68	4.591%	$158.6436	$158.64	$158.65	$158.60
Purchase #5	$19.39	7.781%	$20.8987	$20.90	$20.90	$20.90
Purchase #6	$156.30	6.801%	$166.93	$166.93	$166.95	$166.90
Purchase #7	$129.54	8.658%	$140.7556	$140.76	$140.75	$140.80
7 purchase totals =	$1,063.49		$1,143.5028	$1,143.51	$1,143.55	$1,143.50