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	$5.41	10.550%	$5.9808	$5.98	$6.00	$6.00
Purchase #2	$46.95	12.706%	$52.9155	$52.92	$52.90	$52.90
Purchase #3	$76.99	4.104%	$80.1497	$80.15	$80.15	$80.10
Purchase #4	$84.51	5.375%	$89.0524	$89.05	$89.05	$89.10
Purchase #5	$106.71	10.194%	$117.588	$117.59	$117.60	$117.60
Purchase #6	$56.90	13.159%	$64.3875	$64.39	$64.40	$64.40
Purchase #7	$188.89	8.780%	$205.4745	$205.47	$205.45	$205.50
7 purchase totals =	$566.36		$615.5484	$615.55	$615.55	$615.60