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	$76.84	4.767%	$80.503	$80.50	$80.50	$80.50
Purchase #2	$120.99	13.284%	$137.0623	$137.06	$137.05	$137.10
Purchase #3	$105.86	6.621%	$112.869	$112.87	$112.85	$112.90
Purchase #4	$98.36	7.520%	$105.7567	$105.76	$105.75	$105.80
Purchase #5	$38.54	12.161%	$43.2268	$43.23	$43.25	$43.20
Purchase #6	$240.97	12.247%	$270.4816	$270.48	$270.50	$270.50
Purchase #7	$217.25	9.826%	$238.597	$238.60	$238.60	$238.60
7 purchase totals =	$898.81		$988.4964	$988.50	$988.50	$988.60