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	$45.59	12.829%	$51.4387	$51.44	$51.45	$51.40
Purchase #2	$124.27	4.779%	$130.2089	$130.21	$130.20	$130.20
Purchase #3	$79.66	8.379%	$86.3347	$86.33	$86.35	$86.30
Purchase #4	$74.37	10.722%	$82.344	$82.34	$82.35	$82.30
Purchase #5	$141.82	13.768%	$161.3458	$161.35	$161.35	$161.30
Purchase #6	$192.97	3.865%	$200.4283	$200.43	$200.45	$200.40
Purchase #7	$144.89	5.299%	$152.5677	$152.57	$152.55	$152.60
7 purchase totals =	$803.57		$864.6681	$864.67	$864.70	$864.50