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	$102.51	3.494%	$106.0917	$106.09	$106.10	$106.10
Purchase #2	$83.41	12.567%	$93.8921	$93.89	$93.90	$93.90
Purchase #3	$117.63	8.173%	$127.2439	$127.24	$127.25	$127.20
Purchase #4	$229.73	13.117%	$259.8637	$259.86	$259.85	$259.90
Purchase #5	$39.76	6.589%	$42.3798	$42.38	$42.40	$42.40
Purchase #6	$10.73	3.421%	$11.0971	$11.10	$11.10	$11.10
Purchase #7	$33.92	11.745%	$37.9039	$37.90	$37.90	$37.90
7 purchase totals =	$617.69		$678.4722	$678.46	$678.50	$678.50