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	$99.88	4.662%	$104.5364	$104.54	$104.55	$104.50
Purchase #2	$85.50	9.774%	$93.8568	$93.86	$93.85	$93.90
Purchase #3	$162.58	7.551%	$174.8564	$174.86	$174.85	$174.90
Purchase #4	$250.49	9.789%	$275.0105	$275.01	$275.00	$275.00
Purchase #5	$173.53	10.832%	$192.3268	$192.33	$192.35	$192.30
Purchase #6	$87.50	5.782%	$92.5593	$92.56	$92.55	$92.60
Purchase #7	$152.53	9.231%	$166.61	$166.61	$166.60	$166.60
7 purchase totals =	$1,012.01		$1,099.7562	$1,099.77	$1,099.75	$1,099.80