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	$122.41	13.294%	$138.6832	$138.68	$138.70	$138.70
Purchase #2	$129.28	10.572%	$142.9475	$142.95	$142.95	$142.90
Purchase #3	$82.44	9.687%	$90.426	$90.43	$90.45	$90.40
Purchase #4	$244.85	3.835%	$254.24	$254.24	$254.25	$254.20
Purchase #5	$50.39	13.191%	$57.0369	$57.04	$57.05	$57.00
Purchase #6	$125.90	9.566%	$137.9436	$137.94	$137.95	$137.90
Purchase #7	$186.80	6.334%	$198.6319	$198.63	$198.65	$198.60
7 purchase totals =	$942.07		$1,019.9091	$1,019.91	$1,020.00	$1,019.70