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	$32.51	12.523%	$36.5812	$36.58	$36.60	$36.60
Purchase #2	$137.70	9.102%	$150.2335	$150.23	$150.25	$150.20
Purchase #3	$72.94	7.596%	$78.4805	$78.48	$78.50	$78.50
Purchase #4	$214.34	4.696%	$224.4054	$224.41	$224.40	$224.40
Purchase #5	$179.85	11.468%	$200.4752	$200.48	$200.50	$200.50
Purchase #6	$152.89	7.789%	$164.7986	$164.80	$164.80	$164.80
Purchase #7	$18.27	8.168%	$19.7623	$19.76	$19.75	$19.80
7 purchase totals =	$808.50		$874.7367	$874.74	$874.80	$874.80