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	$236.80	5.529%	$249.8927	$249.89	$249.90	$249.90
Purchase #2	$153.30	6.304%	$162.964	$162.96	$162.95	$163.00
Purchase #3	$50.58	3.142%	$52.1692	$52.17	$52.15	$52.20
Purchase #4	$106.34	12.295%	$119.4145	$119.41	$119.40	$119.40
Purchase #5	$133.79	6.861%	$142.9693	$142.97	$142.95	$143.00
Purchase #6	$54.34	5.836%	$57.5113	$57.51	$57.50	$57.50
Purchase #7	$52.43	13.169%	$59.3345	$59.33	$59.35	$59.30
7 purchase totals =	$787.58		$844.2555	$844.24	$844.20	$844.30