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	$175.50	13.789%	$199.6997	$199.70	$199.70	$199.70
Purchase #2	$166.28	12.187%	$186.5445	$186.54	$186.55	$186.50
Purchase #3	$204.50	10.801%	$226.588	$226.59	$226.60	$226.60
Purchase #4	$31.56	13.760%	$35.9027	$35.90	$35.90	$35.90
Purchase #5	$207.51	11.160%	$230.6681	$230.67	$230.65	$230.70
Purchase #6	$90.97	12.511%	$102.3513	$102.35	$102.35	$102.40
Purchase #7	$79.44	13.383%	$90.0715	$90.07	$90.05	$90.10
7 purchase totals =	$955.76		$1,071.8258	$1,071.82	$1,071.80	$1,071.90