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	$249.77	12.244%	$280.3518	$280.35	$280.35	$280.40
Purchase #2	$90.37	9.841%	$99.2633	$99.26	$99.25	$99.30
Purchase #3	$116.77	8.477%	$126.6686	$126.67	$126.65	$126.70
Purchase #4	$141.57	7.796%	$152.6068	$152.61	$152.60	$152.60
Purchase #5	$21.69	10.853%	$24.044	$24.04	$24.05	$24.00
Purchase #6	$242.59	3.552%	$251.2068	$251.21	$251.20	$251.20
Purchase #7	$72.71	6.271%	$77.2696	$77.27	$77.25	$77.30
7 purchase totals =	$935.47		$1,011.4109	$1,011.41	$1,011.35	$1,011.50