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	$206.96	13.354%	$234.5974	$234.60	$234.60	$234.60
Purchase #2	$196.48	13.458%	$222.9223	$222.92	$222.90	$222.90
Purchase #3	$82.27	8.434%	$89.2087	$89.21	$89.20	$89.20
Purchase #4	$121.92	6.177%	$129.451	$129.45	$129.45	$129.50
Purchase #5	$101.50	9.435%	$111.0765	$111.08	$111.10	$111.10
Purchase #6	$209.42	10.375%	$231.1473	$231.15	$231.15	$231.10
Purchase #7	$92.41	12.802%	$104.2403	$104.24	$104.25	$104.20
7 purchase totals =	$1,010.96		$1,122.6435	$1,122.65	$1,122.65	$1,122.60