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	$26.94	5.249%	$28.3541	$28.35	$28.35	$28.40
Purchase #2	$68.59	6.645%	$73.1478	$73.15	$73.15	$73.10
Purchase #3	$113.82	12.701%	$128.2763	$128.28	$128.30	$128.30
Purchase #4	$208.94	4.464%	$218.2671	$218.27	$218.25	$218.30
Purchase #5	$192.41	12.569%	$216.594	$216.59	$216.60	$216.60
Purchase #6	$73.54	11.584%	$82.0589	$82.06	$82.05	$82.10
Purchase #7	$47.83	9.560%	$52.4025	$52.40	$52.40	$52.40
7 purchase totals =	$732.07		$799.1007	$799.10	$799.10	$799.20