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	$59.26	8.616%	$64.3658	$64.37	$64.35	$64.40
Purchase #2	$73.85	8.136%	$79.8584	$79.86	$79.85	$79.90
Purchase #3	$178.46	3.735%	$185.1255	$185.13	$185.15	$185.10
Purchase #4	$67.26	10.276%	$74.1716	$74.17	$74.15	$74.20
Purchase #5	$117.99	4.215%	$122.9633	$122.96	$122.95	$123.00
Purchase #6	$83.58	3.432%	$86.4485	$86.45	$86.45	$86.40
Purchase #7	$49.42	10.465%	$54.5918	$54.59	$54.60	$54.60
7 purchase totals =	$629.82		$667.5249	$667.53	$667.50	$667.60