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	$168.68	12.256%	$189.3534	$189.35	$189.35	$189.40
Purchase #2	$168.94	6.144%	$179.3197	$179.32	$179.30	$179.30
Purchase #3	$27.63	6.187%	$29.3395	$29.34	$29.35	$29.30
Purchase #4	$143.62	7.867%	$154.9186	$154.92	$154.90	$154.90
Purchase #5	$71.72	11.642%	$80.0696	$80.07	$80.05	$80.10
Purchase #6	$180.92	5.298%	$190.5051	$190.51	$190.50	$190.50
Purchase #7	$14.30	11.215%	$15.9037	$15.90	$15.90	$15.90
7 purchase totals =	$775.81		$839.4096	$839.41	$839.35	$839.40