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	$30.94	3.344%	$31.9746	$31.97	$31.95	$32.00
Purchase #2	$166.43	11.295%	$185.2283	$185.23	$185.25	$185.20
Purchase #3	$215.31	10.784%	$238.529	$238.53	$238.55	$238.50
Purchase #4	$66.51	12.625%	$74.9069	$74.91	$74.90	$74.90
Purchase #5	$142.83	9.537%	$156.4517	$156.45	$156.45	$156.50
Purchase #6	$116.78	8.842%	$127.1057	$127.11	$127.10	$127.10
Purchase #7	$35.91	11.259%	$39.9531	$39.95	$39.95	$40.00
7 purchase totals =	$774.71		$854.1493	$854.15	$854.15	$854.20