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	$156.55	6.698%	$167.0357	$167.04	$167.05	$167.00
Purchase #2	$17.74	13.510%	$20.1367	$20.14	$20.15	$20.10
Purchase #3	$245.58	8.504%	$266.4641	$266.46	$266.45	$266.50
Purchase #4	$84.55	6.785%	$90.2867	$90.29	$90.30	$90.30
Purchase #5	$31.83	12.824%	$35.9119	$35.91	$35.90	$35.90
Purchase #6	$172.76	10.773%	$191.3714	$191.37	$191.35	$191.40
Purchase #7	$187.89	10.289%	$207.222	$207.22	$207.20	$207.20
7 purchase totals =	$896.90		$978.4285	$978.43	$978.40	$978.40