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	$206.40	6.740%	$220.3114	$220.31	$220.30	$220.30
Purchase #2	$127.31	3.281%	$131.487	$131.49	$131.50	$131.50
Purchase #3	$19.57	10.400%	$21.6053	$21.61	$21.60	$21.60
Purchase #4	$238.84	7.499%	$256.7506	$256.75	$256.75	$256.80
Purchase #5	$174.27	4.213%	$181.612	$181.61	$181.60	$181.60
Purchase #6	$81.55	9.748%	$89.4995	$89.50	$89.50	$89.50
Purchase #7	$24.48	10.627%	$27.0815	$27.08	$27.10	$27.10
7 purchase totals =	$872.42		$928.3473	$928.35	$928.35	$928.40