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	$195.27	8.116%	$211.1181	$211.12	$211.10	$211.10
Purchase #2	$96.82	7.837%	$104.4078	$104.41	$104.40	$104.40
Purchase #3	$23.67	3.268%	$24.4435	$24.44	$24.45	$24.40
Purchase #4	$217.27	9.799%	$238.5603	$238.56	$238.55	$238.60
Purchase #5	$53.70	5.855%	$56.8441	$56.84	$56.85	$56.80
Purchase #6	$144.75	13.649%	$164.5069	$164.51	$164.50	$164.50
Purchase #7	$80.51	11.200%	$89.5271	$89.53	$89.55	$89.50
7 purchase totals =	$811.99		$889.4078	$889.41	$889.40	$889.30