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	$25.25	12.701%	$28.457	$28.46	$28.45	$28.50
Purchase #2	$85.55	11.479%	$95.3703	$95.37	$95.35	$95.40
Purchase #3	$155.32	13.422%	$176.1671	$176.17	$176.15	$176.20
Purchase #4	$67.34	5.199%	$70.841	$70.84	$70.85	$70.80
Purchase #5	$95.35	4.725%	$99.8553	$99.86	$99.85	$99.90
Purchase #6	$61.88	12.428%	$69.5704	$69.57	$69.55	$69.60
Purchase #7	$153.31	9.468%	$167.8254	$167.83	$167.85	$167.80
7 purchase totals =	$644.00		$708.0865	$708.10	$708.05	$708.20