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	$116.90	9.333%	$127.8103	$127.81	$127.80	$127.80
Purchase #2	$145.65	13.572%	$165.4176	$165.42	$165.40	$165.40
Purchase #3	$213.38	9.194%	$232.9982	$233.00	$233.00	$233.00
Purchase #4	$29.35	5.296%	$30.9044	$30.90	$30.90	$30.90
Purchase #5	$123.54	6.301%	$131.3243	$131.32	$131.30	$131.30
Purchase #6	$62.75	10.553%	$69.372	$69.37	$69.35	$69.40
Purchase #7	$98.52	11.141%	$109.4961	$109.50	$109.50	$109.50
7 purchase totals =	$790.09		$867.3229	$867.32	$867.25	$867.30