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	$172.34	7.506%	$185.2758	$185.28	$185.30	$185.30
Purchase #2	$248.71	13.696%	$282.7733	$282.77	$282.75	$282.80
Purchase #3	$40.97	3.428%	$42.3745	$42.37	$42.35	$42.40
Purchase #4	$86.83	3.597%	$89.9533	$89.95	$89.95	$90.00
Purchase #5	$47.74	9.332%	$52.1951	$52.20	$52.20	$52.20
Purchase #6	$198.88	12.561%	$223.8613	$223.86	$223.85	$223.90
Purchase #7	$21.31	8.246%	$23.0672	$23.07	$23.05	$23.10
7 purchase totals =	$816.78		$899.5005	$899.50	$899.45	$899.70