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	$245.99	9.345%	$268.9778	$268.98	$269.00	$269.00
Purchase #2	$36.54	10.705%	$40.4516	$40.45	$40.45	$40.50
Purchase #3	$60.69	11.452%	$67.6402	$67.64	$67.65	$67.60
Purchase #4	$14.44	9.723%	$15.844	$15.84	$15.85	$15.80
Purchase #5	$41.43	5.799%	$43.8325	$43.83	$43.85	$43.80
Purchase #6	$127.81	9.151%	$139.5059	$139.51	$139.50	$139.50
Purchase #7	$83.31	10.565%	$92.1117	$92.11	$92.10	$92.10
7 purchase totals =	$610.21		$668.3637	$668.36	$668.40	$668.30