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	$241.30	6.375%	$256.6829	$256.68	$256.70	$256.70
Purchase #2	$38.26	9.803%	$42.0106	$42.01	$42.00	$42.00
Purchase #3	$241.95	10.379%	$267.062	$267.06	$267.05	$267.10
Purchase #4	$149.93	12.459%	$168.6098	$168.61	$168.60	$168.60
Purchase #5	$53.53	11.350%	$59.6057	$59.61	$59.60	$59.60
Purchase #6	$101.35	9.139%	$110.6124	$110.61	$110.60	$110.60
Purchase #7	$27.46	10.491%	$30.3408	$30.34	$30.35	$30.30
7 purchase totals =	$853.78		$934.9242	$934.92	$934.90	$934.90