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	$152.78	6.606%	$162.8726	$162.87	$162.85	$162.90
Purchase #2	$84.78	10.223%	$93.4471	$93.45	$93.45	$93.40
Purchase #3	$28.48	7.392%	$30.5852	$30.59	$30.60	$30.60
Purchase #4	$27.54	7.543%	$29.6173	$29.62	$29.60	$29.60
Purchase #5	$37.27	13.782%	$42.4066	$42.41	$42.40	$42.40
Purchase #6	$17.88	13.795%	$20.3465	$20.35	$20.35	$20.30
Purchase #7	$239.28	9.747%	$262.6026	$262.60	$262.60	$262.60
7 purchase totals =	$588.01		$641.8779	$641.89	$641.85	$641.80