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	$167.27	6.754%	$178.5674	$178.57	$178.55	$178.60
Purchase #2	$50.74	9.436%	$55.5278	$55.53	$55.55	$55.50
Purchase #3	$76.55	8.684%	$83.1976	$83.20	$83.20	$83.20
Purchase #4	$50.88	3.564%	$52.6934	$52.69	$52.70	$52.70
Purchase #5	$94.75	3.372%	$97.945	$97.95	$97.95	$97.90
Purchase #6	$37.27	5.385%	$39.277	$39.28	$39.30	$39.30
Purchase #7	$86.93	4.331%	$90.6949	$90.69	$90.70	$90.70
7 purchase totals =	$564.39		$597.9031	$597.91	$597.95	$597.90