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	$5.33	13.860%	$6.0687	$6.07	$6.05	$6.10
Purchase #2	$87.28	3.443%	$90.2851	$90.29	$90.30	$90.30
Purchase #3	$153.45	11.470%	$171.0507	$171.05	$171.05	$171.10
Purchase #4	$240.42	10.677%	$266.0896	$266.09	$266.10	$266.10
Purchase #5	$61.88	7.541%	$66.5464	$66.55	$66.55	$66.50
Purchase #6	$32.91	10.436%	$36.3445	$36.34	$36.35	$36.30
Purchase #7	$18.57	8.630%	$20.1726	$20.17	$20.15	$20.20
7 purchase totals =	$599.84		$656.5576	$656.56	$656.55	$656.60