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	$82.57	12.485%	$92.8789	$92.88	$92.90	$92.90
Purchase #2	$146.39	3.727%	$151.846	$151.85	$151.85	$151.80
Purchase #3	$76.63	6.546%	$81.6462	$81.65	$81.65	$81.60
Purchase #4	$87.88	13.451%	$99.7007	$99.70	$99.70	$99.70
Purchase #5	$80.56	13.644%	$91.5516	$91.55	$91.55	$91.60
Purchase #6	$150.96	5.330%	$159.0062	$159.01	$159.00	$159.00
Purchase #7	$95.96	4.623%	$100.3962	$100.40	$100.40	$100.40
7 purchase totals =	$720.95		$777.0258	$777.04	$777.05	$777.00