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	$73.86	6.334%	$78.5383	$78.54	$78.55	$78.50
Purchase #2	$61.71	12.725%	$69.5626	$69.56	$69.55	$69.60
Purchase #3	$70.40	8.280%	$76.2291	$76.23	$76.25	$76.20
Purchase #4	$135.92	9.455%	$148.7712	$148.77	$148.75	$148.80
Purchase #5	$127.89	13.109%	$144.6551	$144.66	$144.65	$144.70
Purchase #6	$36.66	6.456%	$39.0268	$39.03	$39.05	$39.00
Purchase #7	$63.28	10.384%	$69.851	$69.85	$69.85	$69.90
7 purchase totals =	$569.72		$626.6341	$626.64	$626.65	$626.70