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	$245.77	13.559%	$279.094	$279.09	$279.10	$279.10
Purchase #2	$73.69	11.444%	$82.1231	$82.12	$82.10	$82.10
Purchase #3	$250.46	9.317%	$273.7954	$273.80	$273.80	$273.80
Purchase #4	$31.88	11.521%	$35.5529	$35.55	$35.55	$35.60
Purchase #5	$250.58	13.437%	$284.2504	$284.25	$284.25	$284.30
Purchase #6	$167.79	3.596%	$173.8237	$173.82	$173.80	$173.80
Purchase #7	$24.55	13.486%	$27.8608	$27.86	$27.85	$27.90
7 purchase totals =	$1,044.72		$1,156.5003	$1,156.49	$1,156.45	$1,156.60