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	$189.73	8.729%	$206.2915	$206.29	$206.30	$206.30
Purchase #2	$99.37	7.641%	$106.9629	$106.96	$106.95	$107.00
Purchase #3	$119.52	6.653%	$127.4717	$127.47	$127.45	$127.50
Purchase #4	$54.69	8.819%	$59.5131	$59.51	$59.50	$59.50
Purchase #5	$120.79	12.605%	$136.0156	$136.02	$136.00	$136.00
Purchase #6	$91.79	9.195%	$100.2301	$100.23	$100.25	$100.20
Purchase #7	$170.54	3.299%	$176.1661	$176.17	$176.15	$176.20
7 purchase totals =	$846.43		$912.6510	$912.65	$912.60	$912.70