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	$69.55	13.508%	$78.9448	$78.94	$78.95	$78.90
Purchase #2	$186.75	9.407%	$204.3176	$204.32	$204.30	$204.30
Purchase #3	$73.76	11.286%	$82.0846	$82.08	$82.10	$82.10
Purchase #4	$35.45	13.823%	$40.3503	$40.35	$40.35	$40.40
Purchase #5	$209.38	6.231%	$222.4265	$222.43	$222.45	$222.40
Purchase #6	$82.44	8.229%	$89.224	$89.22	$89.20	$89.20
Purchase #7	$192.96	12.473%	$217.0279	$217.03	$217.05	$217.00
7 purchase totals =	$850.29		$934.3757	$934.37	$934.40	$934.30