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	$221.85	12.694%	$250.0116	$250.01	$250.00	$250.00
Purchase #2	$125.43	9.663%	$137.5503	$137.55	$137.55	$137.60
Purchase #3	$112.45	4.351%	$117.3427	$117.34	$117.35	$117.30
Purchase #4	$231.64	5.656%	$244.7416	$244.74	$244.75	$244.70
Purchase #5	$90.38	6.360%	$96.1282	$96.13	$96.15	$96.10
Purchase #6	$72.70	6.638%	$77.5258	$77.53	$77.55	$77.50
Purchase #7	$112.82	12.605%	$127.041	$127.04	$127.05	$127.00
7 purchase totals =	$967.27		$1,050.3412	$1,050.34	$1,050.40	$1,050.20