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	$173.53	7.714%	$186.9161	$186.92	$186.90	$186.90
Purchase #2	$241.61	5.579%	$255.0894	$255.09	$255.10	$255.10
Purchase #3	$37.60	7.856%	$40.5539	$40.55	$40.55	$40.60
Purchase #4	$222.43	7.380%	$238.8453	$238.85	$238.85	$238.80
Purchase #5	$57.53	13.156%	$65.0986	$65.10	$65.10	$65.10
Purchase #6	$229.74	3.566%	$237.9325	$237.93	$237.95	$237.90
Purchase #7	$35.74	7.324%	$38.3576	$38.36	$38.35	$38.40
7 purchase totals =	$998.18		$1,062.7934	$1,062.80	$1,062.80	$1,062.80