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	$158.69	13.111%	$179.4958	$179.50	$179.50	$179.50
Purchase #2	$61.83	5.690%	$65.3481	$65.35	$65.35	$65.30
Purchase #3	$73.97	10.847%	$81.9935	$81.99	$82.00	$82.00
Purchase #4	$116.90	9.503%	$128.009	$128.01	$128.00	$128.00
Purchase #5	$125.60	9.534%	$137.5747	$137.57	$137.55	$137.60
Purchase #6	$149.57	10.666%	$165.5231	$165.52	$165.50	$165.50
Purchase #7	$88.40	3.870%	$91.8211	$91.82	$91.80	$91.80
7 purchase totals =	$774.96		$849.7653	$849.76	$849.70	$849.70